As far as software bugs go, this one is monumental. Neowin is reporting that a new bug in Apple's latest Operating System - Snow Leopard - will cause users to loose all their data.

Apparently this isn't just personal settings and preferences, it's actually all data including documents, photos, videos, music and more. The problem occurs when a user logs into the guest account and then back into a regular account, after which they will find said account has been fully wiped clean as if it were a brand new account.

"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."

Way to keep your customers up to date there, Apple. If you're running Snow Leopard you'd be best to disable the guest account just in case you accidentally go in there. And if you haven't already done so - make backups to a separate drive.