I’m using a reseller CPANEL/WHM package from Blurstorm and the same thing happened to me. Yesterday I went to log in to my WordPress blog and all I got was a blank page. I checked source and found a bunch of ad links in there essentially breaking the page. Checking the files the index.php in admin folder had been replaced the day before.
My blog is running 2.7 beta 3 so I downloaded the package and re-uploaded the original index which fixed it.
Today my blog is white and the same crap appears in the front page source. This is what I see.
<!– ~ –><u style=display:none>
[usual drug-related spam links removed]
Checking the index file it also shows as being replaced 11/24/08 which makes no sense since I checked the site yesterday. The index.php file is 6kb in size too instead of 397 bytes. After replacing the index.php my site is completely messed up! I don’t understand what is going on but it’s obvious someone is attacking our web sites.