It's probably being recreated. There may be another process recreating the application, or, in a more extreme case, a driver. Take a look at all the start up processes(via msconfig, or other software).
Generally, a 'virus' which may be in the form of a driver, will have a counterpart, in the form of an executable. This is because many tasks can be perform in user-mode that cannot be performed in kernel-mode.
Chances are it's a keylogger or trojan of some sort, in thus case, I'd just reformat. Can never be too careful with that shiz.