HDD filling up w/o input

Last year I bought a used T61, and installed Vista. Slowly, but surly, the HDD started filling up beyond what was being installed. The HDD would spin w/o input for long periods of time. Thought some of it might be the disk defrag running in the background. Last week it had less than 5gig (of 100gig) and I don't D/L much or store video files. Finally just went back to square one using restore, as the HDD was too full to install 7. Installed 7, firefox, and an often used client (inSSIDer as well but it needs MS net4). Left it alone, except for browsing and client use(no significant data size), yet 200meg of HDD space has been eaten up already.
I have done a malware inspection in the past on a different PC running XP, but am wondering if this could be a root kit? or something similar as it was purchased used and a reinstall seems to have had no effect. Any tips would be greatly appreciated.

 

If you suspect malware, head over here and run the programs and post the findings as per instructions if anything is found.

 

I wiped the HDD, so how does malware survive a format? I can understand root kits surviving a wipe, but malware??
Tell me something I don't know to justify that much trouble, first.

 

Isn't a root kit malware? The volunteers at the malware forum may be able to help you remove it/them if found after doing Read and Run Me First. Yeah, it seems a pita, but the steps are necessary to identify the exact malware the volunteers are dealing with. One or more will have had experience and can tell you what you need to do.

Satrow is a malware removal expert and may be the person who responds to your post in the Malware Removal Forum.

BTW, the Softpedia News Post that plodr posted a link to is from March 25, 2009 so, malware that can survive an HDD wipe has been around for over four years!

 

Well I haven't had any problems for about 7yrs, so sorta out of the loop:-o

And never considered root kits to be malware, guess everything is considered malware.

Thank you for the responses.