Malware that invisibly uses hard drive space?

I also posted on this the hardware thread. But then I contacted HP & they suggested this may be a malware problem. On the outside chance HP is just blowing smoke, I thought I'd ask for advice before I get bogged down in malware removal on a machine that I thought was very clean.

Has anyone heard of malware capable of doing the following:
When I do right click->Properties of my C:, it says that there is 128 GB space used. When I open the C: and select all files then right click->Properties, it says 33.5 GB space used. I am showing all hidden & system files.

TIA as always,
Anne

 

No, I'm not, but I did wind up finding it.

I was going to just backup my docs & re-format. When I went to do the backup, it came to my attention that that's where all the storage issues were.

Turns out that in Docs & Settings there is a Compaq_Owner folder that was hogging everything. I had to take ownership of the folder and then I was able to delete almost all of it (except a few subfolders in Application Data\Microsoft\Installer). Now I've got 107 GB free.

Thanks,
Anne