Have a hidden file that restores the entire virus even if you erase all the other parts.
I even came across one that conneceted to a particular website every time I went online and redownloaded new versions of itself. The actual virus program wasn't even on my computer. I found out when I got an error message naming the website after I cut off the connection.
Try restoring your system to a date before the virus appeared. Also try erasing and reinstalling both Windows and IE.