A Facebook user logged into Facebook from their mobile phone and gained access to another Facebook user's account. The user was an AT&T subscriber, and a glitch in the network was the cause of the identity violation--revealing a very disconcerting flaw in security for the mobile web.
Currently it is unknown just how common (or uncommon) this error is. The access data mix-up may be an extremely rare flaw based on an extreme set of conditions or it could simply be under-reported. Some security experts have also noted that this flaw is possible with email and also with PCs as well.
AT&T commented on this issue stating that the network problem behind it is being fixed. This is not to say that other similar glitches may not arise as internet connectivity demands grow.