If you've not heard (somehow you must be excluded from the world at present!), Dreamhost was hacked and a major number of sites seemed effected. They're still working out how it happened at the moment, but it seems to be a more serious exploit than first imagined. If you google this URL then you'll see a lot of results for the type of attack that was used.

Seems it traverses through the server hard disk for any index.php or index.html files, then inserts a bunch of spam links into the bottom of the files. The more worrying thing, is that this seems like a very large scale attack which was automated.