I just remembered something about .htaccess
I know that it sounded familiar to me...
I got this a few weeks ago for my webhoster :
In our ongoing commitment to the security of our customers, we have discovered a vulnerability located within many of our client's websites, including yours. This is a self replicating virus which is found by visiting well-known search engines. When you click on any link it may redirect you to a fake Anti-Virus 2009 website which appears to scan your system and then asks you to download the software. Once downloaded and installed it begins displaying pop ups on your desktop. At this time it collects your FTP user name and password from your own computer and uses that information to upload an exploited file named ".htaccess" to your website. Any visitors to your website will then be redirected to the fake anti-virus website.
Any clue on this ? Should it be the problem then ?
I never downloaded that software, so it's strange that this hidden file should be on my website...
Whatever, I'll go and create a trouble ticket at my webhoster... I'll let you know the result. :S