Hey guys, I'm currently running Windows 7 x64 Release Candidate. My primary HDD (the one with the problem) is a Western Digital 320GB SATA II.
I have been downloading lot's of stuff lately and just today I looked at my hard drive meter and noticed that it just turned red and I was quite suprised to find only 28.2 GB left, so I checked my downloads folder as it often builds up for long amounts of time before I organise through it and inevitably put most of the data onto my other hard drive, but then I realised there was only about a gigabyte data in it. So I then went into my C drive, and added up the size of all the folders there and they added up to 252GB. So then I go to my C drives properties and it says there is 264GB being used. ?? The recycle bin is empty and I am the only one with an account on the computer.
Any ideas?

Bad news is that there is thought to be a virus described as a 'decompression bomb'. http://forums.cnet.com/5208-6132_102-0.html?threadID=293687 is one example. That's quite old now, and refers to XP, but the problem can also be googled in Vista and Win7.

Long time ago, in win XP one could get and infection masquerading as ntoskrnl.exe, which is a critical process in the boot-up cycle of your computer although should never appear in WinTasks whilst under normal circumstances Note: ntoskrnl.exe can be altered by the w32.bolzano and variants. If this process appears in WinTasks, please update your virus definitions immediately

I don't know if that is true, but the other solutions depend upon cutting down Windows7 expenditure on system restore space. I would also point out that a release candidate by it's very nature is designed to create loads and loads of logging information. You really cannot expect too much from what is not the official release.

Thanks for the info and yeah it doesn't worry me too much as I was planning on installing the full version soon anyway, but I was curious. Just a question though, if it was something like a decompression bomb or big logging file, wouldn't that be counted when I add up the space of all the files and folders in the C drive folder? (noting that I have hidden files set to show)

you know, I had this same prob on my Tb drive, ran a bunch of stuff on it, finally found my solution- reformat xD

Thanks Mictlantecuhtli I'll try that one. Also yangly, I'm probably gonna end up reformatting soon as I move to the real Win7 so hopefully that will fix it up