More than likely, if they have access to your computer, they'll fill a hidden directory with a bunch of similar files. Picture (.jpg), movie (avi, mpg, mp4), or archive (zip, rar) files. If you see a file that you don't know what it does simply look it up on Google. That should give you some idea if it belongs or not. If you're still not sure but want to get rid of it, move it to a temp directory instead of deleting it. That way if something screws up you can move it back.