Here is a bump.
Don't overlook that the HDD may be heading for a failure. Check the logs. SMART is not always a reliable predictor of a looming failure.
Defrag does re-write much of the HDD. However, much of the OS is not affected.
Investing in another HDD is cheap insurance. Move everything to the replacement, then re-format the old drive.
Malware Removal Procedure (
http://www.techspot.com/vb/topic58138.html) has links for Cleaners & HJT that can be used for "tune ups".