Users of Apple's Snow Leopard have reported that their personal data has been deleted when they have logged in using a guest account.
According to a thread on Apple's support forum, the bug resets all settings on the Mac, resets all applications' settings, and erases the contents of critical folders containing documents, photos and music.
PC World claimed that Snow Leopard's home directory, which sports the name of the Mac's primary user, is replaced with a new, empty copy after users log in to a Guest account, log out, then log in to their standard account. All the standard folders - documents, downloads, music, pictures and others - are empty, while the desktop and dock have reverted to an 'out-of-the-box' condition.
One user claimed that he had installed Snow Leopard last weekend and had no major problems but "many annoying bugs", but when he switched it on "the computer had hung - screen saver was frozen. I held down the power key to shutdown. Turned the computer back on, clicked on my user account icon, and it was like I'd just picked up a new computer. My home folder had been replaced with a 'straight out of the box' home folder".
He said he had lost his "standard desktop, standard dock, nothing in my documents folder, standard library. My entire home folder is gone".
Other users also reported the same instance, with one claiming that he "had something very similar happen. I had the guest account enabled on my MacBook Pro - I accidentally clicked on that when I went to log in. It took a few minutes to log in then after I had logged out of that account and back into mine [and] my [entire] home directory had been wiped. All of doc, musics, etc gone".
A report by PC World claimed that the MacFixIt site first reported the problem more than a month ago and reports of the bug go back to September 3, just six days after Apple launched Snow Leopard, or Mac OS X 10.6. Users who said they'd encountered the bug said that they had upgraded their systems from Mac OS X 10.5, known as Leopard.
The thread claimed that some people were able to restore their Macs using recent Time Machine backups, but others admitted that they had not backed up their machines for weeks or months.
In a statement, Apple said: "We are aware of the issue, which occurs only in extremely rare cases, and we are working on a fix."