"Facebook's data feed a data leak?" over at Lawgarithms:
Please correct me if I’m wrong about this; I want to be wrong aboutthis. Or I want to learn that Facebook has already considered and dealtwith the issue and it’s just not readily apparent to me. But I’mthinking that Facebook’s feeds for Status Updates, Notes, and PostedItems must in many instances be at odds with privacy settings thatattempt to limit users’ Facebook activities to “friends only” (or areeven more restrictive).
Denise is both right and wrong. The basic issue is that once you give out a feed URL (which is not guessable) to a friend, they can then give it out to their friends and their friends... ad infinitum. These people can then get your ongoing updates, without you explicitly adding them.
Of course, this requires your friends to breach the trust you placed in them to guard your bits. Notice that even without feeds, your friends can easily copy and paste your bits and send them on manually. It's a simple matter to automate this if a friend really wants to broadcast your private data to whoever they want. So as soon as you open up your data, you are vulnerable to this. To prevent it you'd need working DRM; not a good path to go down.
It would be possible to access control the feeds; there's even a nascent standard (OAuth) for doing this in a secure and standards compliant way. But even this doesn't prevent your friends from copying your bits.
A much simpler approach is to hand out a different URL for each friend. They're still obfuscated of course. You can then block a friend (and anyone they've shared the URL with) from seeing future updates at any time. This is about the best that can be done. Update: This is apparently exactly what Facebook has done. Denise is still concerned that friends could accidentally or purposefully re-share the data, since the feed format makes it easy to do so.
Facebook's messaging could definitely be improved. Suggestions?