Well, you may have a virus, but the DIFX folder is part of the WDK. I doubt a malware writer would use this kit / distributable files to make a malware.
When your system slows down, run a process explorer type of system like System Explorer and see if any strange processes are among the top dozen processes. If so, you are infected and your machine is probably a zombie.
OTOH, you may just have an arthritic Windows setup. The solution to that is to back up your data and then reinstall Windows clean. That will also croak any malwares.