4
I don't think it's the 2.5.0. I have tryed it with another site but the error was at the hostingcompany
Do you have protector-module installed?
Do you have the access logs?
First ting to do, is to change passwords on your FTP account, MYSQL database and so on. (damage-control)
Take a backup of all files, and compare with an ealyer backup - find out what file has changed and what files been add!