since you've deleted said files (yet of course they are still on your HDD) what you can do is this: download, download, download until your drive is almost full...then defragment (this will move data all over and 'organize' it)...basically what will happen is that either the filling of the drive or the defragging will overwrite said offensive files..keep on doing this over a few weeks time, and you will have effectively 'erased' the stuff...

good luck