This is only a suggestion and you may have already done this, but scan your PC and server for viruses and spyware. Then change your FTP password, but not before you do the virus/spyware scan. If the hacker is using FTP to screw up the site, then password protection is useless.
I don't know if 88.118.246.240 is the hackers IP, but if it is, then you could try blocking that IP in the Admin Panel.
Sorry if none of the above helps, but that is all I can suggest.