What's eating the other half of my hard drive?

So a few days ago I noticed I was low on hard drive space. I uninstalled a few things I don't use anymore and freed up about 30GB. 2 days ago I noticed I was low again. I moved some stuff off disk freeing up another 8GB. Last night I noticed I was low again. The partion is actually only using part of the drive (never increased it after moving to a new disk after the old one failed) so I just enlarged the partion by 50GB. I ran some windows updates and was at about 40GB free. I kicked off a disk defragment (defraggler) and went to bed, 8 hours latter came back and I'm down to 4GB. Where is all this space disappearing to? I ran CCleaner, it only found about 100MB (I run it regularly).

So in the last week over 80GB has appeared at best I can explain 1 or 2 GB.

WinDirStat can only find 107GB used in total (i even ran it as administrator) but the drive status says 284GB are used.

What's eating up the other 170GB?

I have hibernate turned off and deleted the hiberfile
I have turned off the paging file and deleted it.
CCleaner can't find anything more to delete.

 

I didn't actually suspect malware, I don't know what the cause is. It's been a while since I had an issue I couldn't figure out on my own and was a little put off when I saw the number of categories here has been significantly reduced since the last time I was here. But now that you mention malware I guess it's possible, I've never heard of malware eating up massive amounts of disk space before though and definitely not in a way that hides it from WinDirStat. I'll run thru those steps when I get a little free time.

 

Sorry, didn't find the forum I needed so just posted in the closest I could and thought windows missbeahving is a little like malware. Anyway while working ouside I got an idea, once I came in I did a google search for why WinDirStat might not be able to find a file. I found a post on another site pointing me at an alternative tool SpaceSniffer. I ran it as administrator (another suggestions from the post) and low and behold it told me the system volume information folder is 181 GB big. A google search on why that happens brought me to system restore settings (http://social.technet.microsoft.com...m-volume-information-folder?forum=w7itproperf) and tada It's using 181 GB and is allowed to use up to 238GB. I lowered it to a more resonable 75 GB and presto I have 126 GB of hard disk free now.

I might run thru all that malware stuff at a latter date (as this system has been off a bit lately) but for now the imediate issue is resolved yay!