something filling up my OS Drive. Please Help

Hi. for the last 3 weeks something has been filling up my C: and I don't know what it is. when I reboot the lost space is back to free space. I have to reboot every 12 hours or so. I have a Sysinternals ProcMon Log for anyone to look at and tell me what the culprit is. WinDirStat doesn't help me just shows unknown as the largest space taken and growing on idle.

Please Help???


Noob Whisperer
Hello and welcome to the forums.
Sounds to me like the behavior of some type of malware.
Maybe grab a blank CD and this program What is Windows Defender Offline? (get the correct version for your architecture) let the program build the bootable CD for you. Boot from the CD and run a FULL system scan. The program I believe defaults to a quick scan, so be sure and run a full system scan after the quick scan has completed.
Additionally grab the free version of MalwareBytes from here Malwarebytes : Malwarebytes Anti-Malware PRO removes malware including viruses, spyware, worms and trojans, plus it protects your computer
Install it, update the signatures, reboot the computer into safemode and run a full system scan with that product as well. If you'd like and you find the product beneficial you can always purchase the PRO version. I did and have never regretted it. I believe this site is part of an affiliate program so you can use this link should you decide to purchase
Good luck and keep us posted.

Hi, I have run Malwarebytes, Hitman Pro, Windows defender offline, CCleaner. and I am still having the same issue. I don't think it's Malware unless it cannot be detected by most of the free and trial versions of most spyware/malware blah blah blah applications.

as I said, if I reboot the space it back and everything runs normal for a while then all of a sudden C: will show as full. sometimes I can watch as GB per second just get used and I'm not running anything but Windows Explorer (Computer drives display).

I am running ZoneAlarm Extreme Security. I just need to find what is writing the big files. I don't have a hibernate file and paging file runs off a second drive.

is there no other way of seeing what application is writing such huge information in such a short time? I am pretty sure it is not malware but of course it could always be, searching for solutions to this problem I have found someone else had an issue with a program writing a corrupted log file and it kept getting massive in a few minutes. I don't have the application he was using but I might have a similar issue. I don't know what to do anymore. So sick of malware and virus crap.

Thanks Again all you guys out there for the help.


Well-Known Member
Try using Directory Report
It scans your computer and shows the size of all folders

You can also see all files in descending size order,
Select menu: Largest / Display Largest Files

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