Details are still sparse (and primarily in Japanese), but our Tokyo bureau just let us know that Sony's announced a fairly severe security vulnerability on the PlayStation Network, which would actually allow an attacker to access your account, personal information, and Wallet -- but not your credit card on file -- as well as change your password. Damn. More on this as it develops; in the mean time, keep a close eye on that account.
Update: More information is on the US PS3 site. Apparently the issue has been resolved and "security is restored." Thanks, luckydude76.