Reports have been cropping up on the Apple Support forums that users have been losing all their data due to a nasty bug in Snow Leopard, Apple's latest Operating System. Many users are reporting that all settings are being reset and most data is gone, according to iTWire.
The problem, can easily be reproduced when a user logs into the 'guest' account, either on purpose or by accident, and when they log back out of the account and back into their normal one, they find that their account has been fully reset with all data wiped and lost - the account is like a brand new one. The home directory still exists under "/Users/username" but is completely empty.
Users are reporting that the data is unrecoverable and cannot be found anywhere on the hard drive, and the only way to restore it is if the user has been performing backups on a separate hard-drive. Apparently the problem has been present since a few days after launch, as the forum post dates back to 12th September, but as of yet, Apple has been silent.
It seems the only work around at this stage is to disable the Guest account, or at least disable it and then re-enabling it so that it's a native Snow Leopard account. Another suggestion is to create a new account and enforce parental controls, if you really need a temporary account.
It's not clear how many users are affected, but it seems like any user who had Leopard before the upgrade, and had the guest account enabled are affected and are at risk.
Update: CNet has published a method to restore the files from a Time Machine backup to a new, identical user profile. If you have lost files due to this problem, and have an intact backup please follow the steps found here - the restore process may take over two hours to complete.
Update #2: Apple has acknowledged the problem to CNet in a prepared statement late yesterday announcing:
"We are aware of the issue, which occurs only in extremely rare cases, and we are working on a fix," an Apple representative said in a prepared statement Monday."
Update #3: For those who are concerned that they could be affected, our recommendation is to disable the guest account fully. If you require it though, make sure you make a complete backup of your hard disk before you try the account again if you upgraded from Leopard to Snow Leopard, just to be safe.