Something I've been worrying about for a long time has just happened: Antisec has leaked a database with more than a million UDIDs. The UDID issue has been a bit of a white whale of mine - I've written many blog posts about it and spent more hours than I care to think negotiating responsible disclosure with companies misusing UDIDs. Let's recap some of the posts I've written about this:
In May 2011, just before its sale to Gree was announced, I showed that OpenFeint was misusing UDIDs in a way that allowed you to link a UDID to a user's identity, geolocation and Facebook and Twitter accounts. I didn't discuss it openly at the time, you could also completely take over an OpenFeint account, and access chat, forums, friends lists, and more using just a UDID. This resulted in a class-action lawsuit against OpenFeint, which has since petered out.
Later that month, I published a survey looking at how UDIDs are used in practice. The data is now slightly out of date, but shows just how widely UDIDs are used and misused.
In September 2011, I published the most troubling news so far, which paradoxically also got the least coverage in the press. I looked at all the gaming social networks on IOS - basically OpenFeint and its competitors - and found catastrophic mismanagement by nearly everyone. The vulnerabilities ranged from de-anonymization, to takeover of the user's gaming social network account, to the ability to completely take over the user's Facebook and Twitter accounts using just a UDID.
As serious these problems are, I'm afraid it's just the tip of the iceberg. Negotiating disclosure and trying to convince companies to fix their problems has taken literally months of my time, so I've stopped publishing on this issue for the moment. It's disheartening to say it, but some of the companies mentioned in my posts still have unfixed problems (they were all notified well in advance of any publication). I will also note ominously that I know of a number of similar vulnerabilities elsewhere in the IOS app ecosystem that I've just not had the time to pursue.
When speaking to people about this, I've often been asked "What's the worst that can happen?". My response was always that the worst case scenario would be if a large database of UDIDs leaked... and here we are.