Posts Tagged ‘iphone’

Smart Phone. Clumsy User

I have learnt four things over the past year or so.

One. The iPhone 3’s glass was scratch resistant but not dropping-onto-a-stone-floor resistant.

Two. I am clumsy.

I Think I Need A New iPhone. Bugger

Three. The iPhone 4’s glass was scratch resistant but not dropping-onto-a-pavement resistant.

Four. I am still clumsy.

FFS. Not Again!

Written and posted from the Nokia gate5 office in Schönhauser Allee, Berlin (52.5308072, 13.4108176)

Farewell Ovi Maps, Hello Nokia Maps (On iOS And Android Too)

In May of this year, Nokia announced the retirement of the Ovi brand and the observant map watchers amongst you may have noticed that pointing your browser of choice at now automagically redirects you to the new, shiny

What you may not have noticed is that Nokia maps doesn’t just work on your desktop or laptop web browser or on Nokia smartphones, as Electric Pig nicely pointed out, Nokia has invaded the iPhone too. Point your iPhone or iPad at the Nokia Maps for Mobile Web at and you’ll see something like this …

Nokia Maps on iOS

… a fully featured version of Nokia Maps that does search, satellite views, GPS and location fixes, navigation, even public transport and, of course …

Nokia Places on iOS

… places. And it’s not just iOS devices that the new Mobile Web maps supports, Android users can have this too as can Blackberry users.

Nokia Maps on Android

That’s not just geo-tastic, it’s geo-egalitarian.

Written and posted from theRadisson Blu hotel, Berlin (52.519648, 13.40258)

iOS Location Caching Round-up – Conspiracy Theories: 0, Smart Location Caching: 1

More a meta post, or what Kuro5hin would have called MLP (meaningless link propagation), this post started out as a comment to one of my previous posts on the iOS location caching controversy but soon expanded way beyond a comment into a full blown post.

Firstly, let’s get the conspiracy theory out of the way; this theory has been presented in a variety of ways but all of them seem to think that your iOS device is tracking your location and that the reason for this is some shadowy request from government or intelligence agencies. Perhaps the most eloquent case for this was on Frank Reiger’s blog.

Now I love a good conspiracy theory as much as the next person and Frank’s blog post was a great read. But I have to take issue with the two main points he raises. Firstly there’s “if it was a bug then it would have been fixed … it hasn’t been fixed so it can’t be a bug and must therefore be deliberate“. Secondly there’s “not only has the bug not been fixed but the file even moved location without being fixed so it must be (even more) deliberate“.

Encyclopedia of Conspiracy Theories

I’ve worked in the software industry for almost 25 years, many of those cutting code, and can say with hand on heart that bugs, oddities and plain wrong behaviour stay in code bases not because they don’t need to be fixed but because other factors push them down in the priority list, factors such as hard release dates, new features taking precedence and the ill defined side effects of complex software systems not being able to be fully QA’d. Just because a bug or an unforeseen side effect remains in a production code base does not make a conspiracy theory of government or intelligence agency intervention.

We also live in a world of distributed software development teams. It’s enough of a challenge to keep teams in different floors of the same building in synch; it’s even more difficult when language, time zones and different countries get into the mix. Just because the consolidated.db cache moved location again, does not make a conspiracy theory.

So all in all, nice post, great conspiracy theory but, sadly, very little to back up the assertions.

But if your iOS device is tracking or caching your location, why is the data so inaccurate in places, showing places you’re pretty sure you haven’t been or have visited only fleetingly, yet not showing places you’d think would show up, such as where you live or work?

For the answer to these questions, I’d recommend a thorough reading of Peter Batty’s excellent three posts on the topic, which actually digs into the data that is present on iOS devices, rather than making shrill conspiracy theories based on other, equally shrill, media headlines.

Peter’s posts, “So actually, Apple isn’t recording your (accurate) iPhone location“, “More on Apple recording your iPhone location history” and “The scoop: Apple’s iPhone is NOT storing your accurate location and NOT storing history” go into great detail about what the consolidated.db location data cache does contain and, more importantly, what it doesn’t.

An anonymous comment on one of Peter’s posts points to a document submitted by Apple to US Congress in July 2010, which includes the following

When a customer requests current location information … Apple will retrieve known locations for nearby cell towers and Wi-Fi access points from its proprietary database and transmit the data back to the device … The device uses the information, along with GPS coordinates (if available), to determine its actual location. Information about the device’s location is not transmitted to Apple, Skyhook or Google. Nor is it transmitted to any third-party application provider, unless the customer expressly consents

Another comment from Jude on one of Peter’s posts makes this observation …

My Guess?

It’s not a list of cell phone locations that you’ve been to, but the opposite, a list of cell phone locations near you downloaded to the iPhone from Apple in case you move into range of one of them. i.e. At a guess what is happening is location services identifies a cell tower and asks for its location, and is replied to with the list of locations that contains that cell tower, that list is then cached so that it does not need to be requested again.

Of course, this is only a guess based on the wide range of addresses people are seeing and how its near to, but not exactly where, the people have traveled.

So rather than iOS actively and accurately tracking you and reporting this information to some, unspecified, intelligence agency it’s actually the complete opposite; your device is actively downloading the next cell tower and, in some cases, wifi information that is near you and where you might be going to provide a better location experience. Which explains the inaccuracy of the locations people have been seeing in their version of the cache data and explains why there’s some places they haven’t been showing up in the data and why places they have been aren’t showing up.

hat Fool Columbus Hasn't Got GPS

Of course, this information still has personal value and should really be secured by iOS and not by an individual having to secure their handset and encrypt their backups but if anyone still thinks they see the black helicopters circling, it looks more and more unlikely and, as Ed Parsons pointed out, a smartphone without location just isn’t … smart.

Photo Credits: Álvaro Ibáñez and Tom Jervis on Flickr.
Written at home (51.427051, -0.333344) and posted from the Nokia gate5 office in Schönhauser Allee, Berlin (52.5308072, 13.4108176)

Location’s “Ick Factor”; First iOS And Now Android

Two days ago I wrote about the “discovery” of a cache file on iOS devices that stores the position of cell towers and the associated media coverage surrounding this. Note that I use “discovery” in inverted commas here. As Sally Applin pointed out in a comment on my previous post, this “discovery” is not new and a paper on this by Alex Levinson, Bill Stackpole and Daryl Johnson was published in January 2011 as part of the Hawaii International Conference on System Sciences. Maybe sometimes researchers don’t read other, existing, research on a subject before publishing.

No matter where you go, there you are. - Buckaroo Bonzai

I’m not the only one to question the media coverage and the conclusions the media presents. Longtime Apple commentator and author Andy Ihnatko neatly sums the entire topic up thus

A few reality checks, lest I inadvertently do a Glenn Beck number on all of you, here:

  • This database isn’t storing GPS data. It’s just making a rough location fix based on nearby cell towers. The database can’t reveal where you were…only that you were in a certain vicinity. Sometimes it’s miles and miles off. This implies that the logfile’s purpose is to track the performance of the phone and the network, and not the movements of the user.
  • A third party couldn’t get access to this file without physical access to your computer or your iPhone. Not unless you’ve jailbroken your iPhone and didn’t bother resetting its remote-access password…or there’s an unpatched exploit that would give Random Person On The Internet root access to your phone.
  • It’s pretty much a non-issue if you’ve clicked the “Encrypt iPhone Backup” option in iTunes. Even with physical access to your desktop, a no-goodnik wouldn’t be able to access the logfile.

But still! What a nervous can of worms. This is an open, unlocked file in a known location in a standard database format that anybody can read. If someone has physical access to your Mac — or remote access to your user account — it’s a simple matter of copying a file and opening it. And while the logfile can’t tell someone that you were at a specific house, it can obviously tell your boss that you went to the Cape on the day you called in sick.

And it’s not as though Apple and these two developers are the only people who know that this file exists and that it’s so easy to access. By the time the Good Guys blow the whistle, the Bad Guys have had it for months. Lord only knows what they’ve been doing with this information.

It’s also, frankly, another reason why I value my iPhone’s “remote nuke” feature and wish it were possible to nuke all data directly from the handset. I can’t think of any circumstance under which my location data would possibly be damaging, incriminating, or even just embarrassing. That’s not the point: if I can’t control the data that my phone is collecting, I should at least have the power to destroy it utterly.

Another well known Apple commentator, John Gruber also comments that

The big question, of course, is why Apple is storing this information. I don’t have a definitive answer, but the best at least somewhat-informed theory I’ve heard is that consolidated.db acts as a cache for location data, and that historical data should be getting culled but isn’t, either due to a bug or, more likely, an oversight. I.e. someone wrote the code to cache location data but never wrote code to cull non-recent entries from the cache, so that a database that’s meant to serve as a cache of your recent location data is instead a persistent log of your location history. I’d wager this gets fixed in the next iOS update.

In my previous post I wrote that “caching is a common technique used to speed up network systems and it’s not surprising, at least to me, that iOS is using caching techniques” and it turns out that iOS is not alone and that, unsurprisingly, Google’s Android is doing pretty much the same thing, caching cell tower and wifi location information, again presumably for the purposes of speeding up the location systems on Android mobile devices. The one difference between the iOS and Android approach is that Android overwrites the cache data when the cache file fills up whereas iOS doesn’t. Rather than a dark location tracking conspiracy this looks more like a bug or an oversight on the part of iOS and as John Gruber notes, this will probably be fixed in an upcoming release of Apple’s mobile operating system. I would also hope that the visibility of this cache data on Android will also be secured too, and soon.

Taking a step back for a moment, caching of any information to reduce the need to make time costly network calls seems to be mobile’s Kobayashi Maru … you’re damned if you do and damned if you don’t. If you do cache information which is perceived, rightly or wrongly, to be sensitive then media outrage will result. If you don’t cache such information, then a mobile device will be reliant on network access every time the un-cached information is needed and that mobile device will be perceived as being “too slow“.

Probably the only way to prevent a recurrence of this sort of media event is for more transparency on how such information is being stored and used and, as John Abbott pointed out on my previous post, the provision of a setting which says “Switch this setting on for a super-quick location fix, we’ll keep your location private“.


As is so often the case, this is much less about the technical side of the issue and much more about what Ihnatko calls the “Ick Factor” … about how the public, led by the media, sees things.

Photo Credits: Stefan Andrej Shambora and Trevin Chow on Flickr.
Written and posted from home (51.427051, -0.333344)

iOS Location “Tracking”; Gross Invasion Of Privacy Or Media Sensationalism?

Oh dear. For a few years now I’ve been talking about how the privacy aspect of today’s location technologies is something that may just catapult location into the mainstream, and possibly tabloid, media and probably for the wrong reasons. I envisaged this as being something salacious and potentially titillating, such as two Z List celebrities involved in a high profile divorce case, where they claimed to be in two separate places but their phone’s A-GPS showed the complete opposite. If you were at Where 2.0 in San Jose this week or reading the headlines on the web sites of the BBC, The Guardian or BoingBoing, you’d be forgiven for thinking that just such a location media event had happened. But has it? The headlines certainly seem to think so …

iPhone tracks users’ movements … says the BBC

iPhone keeps record of everywhere you go … says the Guardian

Got an iPhone or 3G iPad? Apple is recording your moves …. says O’Reilly Radar

iOS devices secretly log and retain record of every place you go … says BoingBoing

… and when I use the word “says” in reality “screams” would be more accurate.

Privacy Area

But as is often the case, the headlines don’t tell the whole story. At Where 2.0 two security researchers have discovered a cache file in iOS which contains cell tower ids and corresponding longitude and latitude coordinates. This cache file isn’t accessible if your iOS device has a passcode lock enabled, which it should be, and while it is backed up to any computer you synch your iOS device with, if your backups are encrypted, which they should be, this cache file isn’t accessible is anyone, especially not “a jealous spouse or private detective” as the researchers claim.

So why is your iOS device caching your cell tower ids and their locations? A reasonable supposition would be to speed up the A-GPS subsystem in your device, so that time consuming network calls don’t always need to be made and so your iOS device seems to be faster. Caching is a common technique used to speed up network systems and it’s not surprising, at least to me, that iOS is using caching techniques.

Massachusetts Ave with iPhone Google Maps

So if you’re an iOS user, should you be worried? It’s true that the iTunes terms of service does say that “We may collect information such as occupation, language, zip code, area code, unique device identifier, location, and the time zone where an Apple product is used so that we can better understand customer behavior and improve our products, services, and advertising” but there’s currently no evidence that location information is actually being sent to Apple as a result of this caching. That’s not to say that it isn’t or that it won’t be in the future, but for now, it looks unlikely. Take some basic security precautions such as a phone passcode lock and encrypt your synchronised backups and this looks less like a gross invasion of privacy and much more like any other use of caching techniques.

Cell Tower Mast

I think it’s right and good that researchers are probing into the the depths of a popular mobile operating system and looking for vulnerabilities. Your location, regardless of whether it’s your current position or where you’ve been is valuable and above all private information and is ripe for abuse as last year’s news on how free Android apps are sharing people’s location without their knowledge shows. But I take issue with the conclusions drawn from such research as this and how it’s being publicised. To put this in context, consider the following, totally imaginary on my part, media headlines about caching …

Your web browser records every web page you visit!

Well yes, but … without this your browser would far less usable and far slower and caching is a fundamental part of how the web works.

Your Internet Service Provider stores copies of every email you send and receive!

Well yes, but … it’s part of the IMAP protocol that most email accounts use today.

Your mobile phone provider tracks your mobile phone’s location!

Well yes, but … it’s the way that cellular networks work. It’s how you can make and receive calls. Disable this and mobile networks stop working.

Finally I’m reminded of the other, media fueled furores, that have appeared and subsequently disappeared, around the launch of Google’s Latitude and Facebook’s Places. Much media coverage ensued, many sensationalistic headlines, much wringing of hands from industry pundits and then the rest of the world got on with using location technologies and didn’t give it a second thought … until the next time the media wants some headline attentions.

Photo Credits: Mark Barkaway, Steve Garfield and Happychopper on Flickr.
Written and posted from home (51.427051, -0.333344)

Adding Windows Phone 7 Support To WordPress Blogs

Regular visitors to the uncharted backwaters of the unfashionable end of the Internet that is my blog may be aware that I use WordPress as a blogging platform. Those visitors who come here via a browser on a phone may even be aware that WordPress automagically presents a mobile friendly version of the site. This magic happens because of the user-agent string your browser sends to the web server hosting my blog; this string tells the web server what sort of browser (and more importantly what sort of device) is trying to view my blog. If WordPress sees a user-agent string like this …

Mozilla/5.0 (Linux; U; Android 2.2; en-us; Nexus One Build/FRF91) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1

… it knows that I’m browsing from my Google Nexus One and serves up the mobile version of the site, but if it sees a user-agent string like this …

Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_6_6; en-us) AppleWebKit/533.19.4 (KHTML, like Gecko) Version/5.0.3 Safari/533.19.4

… it knows that I’m browsing from Safari on a Mac and serves up the normal version of the site. Actually it’s not WordPress that knows how to act on a browser’s user-agent string, it’s a neat WordPress plugin called WPTouch that does the magic.

But then I tried viewing my blog on my new Windows Phone 7 handset and WPTouch doesn’t work its magic.

It turns out that there’s a clue to the solution in the name; WPTouch was designed to serve up the mobile view of a WordPress blog for the iPhone and the iPod Touch. Support was then added for Android and Blackberry handsets, but not for Windows Phone 7. Luckily, the plugin supports custom user-agent strings so adding support for Windows Phone 7 should be trivial. Well maybe not that trivial. A quick web search shows that there’s at least 10 variants of the Windows Phone 7 user-agent.

But rather than list them all explicitly, simply adding “iemobile“, the lowest common denominator, as a custom user-agent string catches them all.

Armed with all this information, my blog now support Windows Phone 7 with ease, plus adding “nokia, symbian” as additional custom user-agent strings means that my Nokia N8 can also view the mobile version of my blog.

As a final footnote, if you’re wondering why I’ve used photos of Windows Phone 7 rather than screenshots, it’s because along with multi-tasking and copy-and-paste, Windows Phone 7 doesn’t currently support taking screen shots. Yet. But then again, the original version of the iPhone lacked a lot of this functionality too, which did nothing to dent the uptake of that handset. Multi-tasking and copy-and-paste is promised in the next upcoming WP 7 OS update, hopefully with screenshot taking as well.

Written and posted from home (51.427051, -0.333344)

A First Step Towards Indoor Navigation. Literally

The problems started the moment GPS became a commodity and made the transition from the car to the mobile device. Nowadays, GPS can be found in a vast range of smartphones and navigation is possible without being confined to your car. Of course, it’s not always a great experience. GPS works best when there’s a direct line of sight to the satellites whizzing around over your head and there are times when you just can’t get a GPS lock. A-GPS was devised to help with such situations, allowing your location enabled to device to take advantage of a variety of other sensors, such as cell tower and wifi triangulation technologies.

But even then, GPS just doesn’t work indoors most of the time and indoor location and routing has become something of the Holy Grail for navigation technology vendors. Granted there have been lots of technologies developed which use non A-GPS technologies such as RFID and other near field sensors. But so far these all require a not insignificant investment to install and require specialist devices to take advantage of; none of which are as ubiquitous as the combination of smart phone and GPS.

Maybe we’re looking too deeply at this challenge. Take a category of location that lots of people go to, such as shopping malls, where GPS usually isn’t available, and map each mall to a high degree of accuracy, both in terms of the layout of the mall and in terms of the stores and concessions in that mall. Add in key features, such as multiple levels, staircases, escalators and lifts and you can build a spatial map of the mall which doesn’t need sensors. Simply tell your phone where you are and where you want to go and you can provide simplistic directions, without the need for GPS.

FastMall - Mall Overview

It’s obvious when you stop to think about it.

Whilst it’s not the voice guided, constantly updated, turn by turn navigation that we’re used to in conventional satnav, as a technology it’s simple to implement and FastMall, an iPhone app, has done just that.

So how does it work? Like most location based apps, FastMall taps into your iPhone’s onboard GPS allowing you to search for malls near to you (as a side note, this location based search isn’t geofenced at all, searching for malls around me in Berlin returns a huge list of European malls). Select the mall you’re either at or are going to and you download the mall’s map and data to your device. At this stage your need for GPS or even for a cellular signal is over. The locations of each store in the mall (even including toilets, staircases and escalators) are now on the phone. Navigating to the store you need is elegantly simplistic; simply tell the app where you want to go and tell the app where you are and you get a (literally) step by step guide to reach your destination.

FastMall - Navigation Setup

Let’s take an example of a mall I know reasonably well; the Westfield Valley Fair mall in Santa Clara, California. I’ve parked my car in the car park next to Macy’s and I want to get to the Apple Store. Assuming I’ve downloaded the mall map data (and this is in the US so there’s no guarantee I can do this in the car park as this is AT&T territory) I simply search for the Apple Store as my destination and then search for Macy’s as my starting point and I’m presented with precise walking directions on how to get there.

  1. Exit Macy’s
  2. Walk until you see Nine West and go straight
  3. Walk until you see Marc Ecko Cut & Sew and turn slight left
  4. Walk until you see Jessica Mcclintock and go straight
  5. Walk until you see MAC Cosmetics and go straight
  6. Walk straight until you see your destination on the right
  7. Enjoy. You have reached Apple Store

FastMall - You Have Reached Your Destination

I’ll forgive the app’s designers the slightly stilted phrasing in the directions but overall the experience is simple and seamless. It doesn’t take a vast leap of the imagination to see this sort of hybrid A-GPS and spatial map technique extended to other types of location, such as railway stations, conference centres and other pedestrian areas.

Now yes, I know this is iPhone only, yes I know this needs a high end smartphone and yes, this would really benefit from being integrated into an overall maps and navigation experience. But it’s a significant step towards real world, usable indoor navigation. Sometimes the simple approach outpaces the technological sensor driven approach we’ve become used to. Expect to see this sort of technology coming your phone in the not too distant future.

Written and posted from the Nokia gate5 office, Invalidenstrasse, Berlin (52.53105, 13.38521)

There Isn’t An App For That

Want to upload photos to multiple social networking and photo sharing sites, such as Flickr and Twitpic? There’s an app for that. Pixelpipe seems to work for me.

Want to update your status on multiple social networking sites, such as Twitter and Facebook? There’s an app for that. Tweetdeck seems to work for me.

There's an App for (almost) everything

Want to check in to multiple place based services, such as Foursquare and Gowalla? There’s an app for that. seems to work for me.

Want to change your profile photo or biographical information for all of your online accounts. There’s an app … oh … wait. There isn’t an app for that. But there’s a app crying out to be written.

Written and posted from the Yahoo! London office (51.5141985, -0.1292006)

Creative Commons in Action

I take a lot of photos, most of which end up on my Flickr photo stream. While some of them are taken with a proper camera  (though some would say that my Lumix FX12 isn’t a proper camera), most of them are taken with my iPhone, which doesn’t take great pictures but takes pictures which are good enough and with the added bonus that I have it on me almost all of the time.

My photos all used to be publicly accessible and with an all rights reserved copyright on them but then I lost my Flickr innocence, which was a bad thing at the time and switched all of my photos to friends and family visibility. About a week later, when I’d calmed down a bit, I went through all of my photo sets; photos of my family and of home stayed out of the public eye and stayed all rights reserved. But everything else, I opened up and changed the license to some rights reserved using the Creative Commons Attribution Share-Alike license.

Royal Festival Hall Lights

The reasoning behind this was that pretty much every slide on every deck I put together has a background from Flickr which is licensed under the Creative Commons model. Without this license and without people releasing their photos using it, my slide decks would be altogether poorer and a whole lot blander.

Opening up some of my photos under Creative Commons works both ways. In February I received a mail from someone at Schmap telling me that two of my, Creative Commons licensed, photos had been shortlisted for including in the next edition of their London guide. Instantly suspicious of this I asked the Twitter-verse for commentary; Vikki Chowney, Lorna Brown and Tim Moore were good enough to respond and tell me that this wasn’t a scam, as my cynical mind had first surmised.

Soba Soba Soba

It’s not much in the grand scheme of things but the people at Schmap either liked the photos I’d taken of the Royal Festival Hall and in Chinatown’s Tokyo Diner (less likely) or didn’t have any other suitable candidates and so plumped for mine (much more likely). Either way, this was a great example of Creative Commons in action and it allows me to continue to mine Flickr’s ever growing pool of photos for my slide decks with a clear conscience.

Written and posted from home (51.427051, -0.333344)

It’s Time to Stop LAMB (Location Based SPAM) Before It Even Exists

We all suffer from SPAM, the unwanted and unsolicited commercial bulk emails that are the reason we have Junk Mail filters and folders in our email clients and servers. A quick glance at the Junk folder for my personal email account shows over 300 of these since the beginning of February alone.

If you use some form of instant messenger, be it MSN, Yahoo!, ICQ, AOL or any of the others on the market, you’ve probably come across SPIM, Instant Messaging SPAM. Then there’s also mobile phone SPAM via text messages, comment SPAM, the list goes on and on.
We’re poised to start seeing a new form of SPAM raise its ugly head. Let’s call it LAMB for now, Location Based Advertising SPAM.
If you build your application with features based on a user’s location, make sure these features provide beneficial information. If your app uses location-based information primarily to enable mobile advertisers to deliver targeted ads based on a user’s location, your app will be returned to you by the App Store Review Team for modification before it can be posted to the App Store.
This is a good first step in locking down potential abuses of a technology before it has a chance to get out of control. The reason we have SPAM and all the other variants in the first place is that the underlying technologies were designed in an open manner with no control mechanisms in place to thwart unsolicited and unwanted messages and content. But we need to go further than this.

The first time you use a location aware app on an iPhone, it asks your permission in nice, unthreatening language; it “would like to use your current location“. What this actually means is that it wants to use, and continue to use, your precise location to the finest level of granularity that the A-GPS system on the phone is able to deliver at the time it’s being requested.
There’s no way of halting this process temporarily, of being your own source of truth for your location (AKA lying about your location) or of controlling this on a per application basis. You can only reset asking this permission for all apps and for the entire phone via the Settings app. Although some well behaved apps such as TweetDeck do allow you to disable use of location information altogether as as well as on a per Tweet basis.

What we really need is to see is a way to set location granularity, including no location information at all, on a per app basis in much the same way as Fire Eagle currently does. And for all apps on all location aware platforms, not just Apple’s and the iPhone’s.

Some may argue that requiring such a degree of choice and intervention by the user may raise the barrier to entry to such a degree that an app doesn’t reach such a large audience. It’s a valid argument but as part of the location industry, I believe that we need to find the middle ground between irking the user once per app and letting LAMB loose on the world which has the possibility of irking the user multiple times per hour.
Written and posted from home (51.427051, -0.333344)

Posted via email from Gary’s Posterous