According to digi.no, wordpress and joomla are under heavy attacks these days. A botnet of around 90.000 computers tries to brute-force the accounts: Admin, Administrator, Root and Test. If any of those matches the username you use on your blog, then you might aswell have been hacked.
Im no computer security expert, so i cant say anything for sure. I know that comments aint disappearing on their own, though.
