Do virus/keyloggers/trojans occupy 100+Mbs of HDD space?

I've discovered something really odd with my system over the past few months. For some time now I've been short of HDD space on my current Vostro (Vista Basic x86) but lately the HDD free space has been spiking a lot.

Last week I had roughly 1GB of free space on my system drive, several days ago I found that free space had suddenly shrunk to less than 100MB free. Since I download a fair amount of videos each week I decided to do some spring-cleaning and moved a few files to my partition which has sufficient space. The odd thing was even after moving 1GB+ of videos my system drive free space refused to go above 200MB+.

The current situation is 200+ MB free HDD space, down more than 50% from the previous night without me doing anything to the drive.

In the past, I've had situations where the HDD space would suddenly shrink of its own accord despite my best attempts to clear files (Disk cleaner, CCleaner etc.) and then magically restore free space on its own without my active intervention. I had previously attributed this to the PC cleaning up cached video files stored onto HDD space for quicker playback, however this doesn't seem right since my last video house-cleaning cleared much less HDD space than what I would have expected.

The recent hacking exploits by Lulzsec and the like have made me somewhat wary that my PC has been hit by something I'm not aware of, but I don't know if a side effect of my PC being hijacked is the occupation of close to 1GB of HDD space. It is getting ridiculous to find my PC still functioning and not crashing even though the HDD metre says I have 0B of free space in my system drive.

 

Its strange that system performance hasn't plummeted, but the best way to find malware is to scan for it.

 

Avira antivirus good enough for the job? I haven't picked up anything from the automatic scan function either.

 

Could simply be temporary folders. If you deleted those videos by sending them to the recycling bin they might have still been taking up some space.

 

I use the Shift-Delete command to get rid of unnecessary videos and move the rest over to external HDDs, anyway both CCleaner and the native disk cleaner tool have been countless times with clean recycle bin option turned on.

 

Avira should be good enough. I would use a second AV to do a second scan as well.

 

You could also take a look at the free version of Malwarebytes : Free anti-malware, anti-virus and spyware removal download

If it doesn't find anything, your computer is fine.

Remember to update it when you've installed it.

 

I think that what you are seeing is the result the OS attempting to manage the fact that you are out of HDD space. Get a bigger hdd.

 

or change/get rid of the partitions.

have you cleared system restore points? they can be huge, and growing.

maybe windirstat will show up a folder with thousands of files, or a folder with a huge file. maybe try that.

 

This was my initial suspicion. Also, you could try a 3rd party defrag tool to see if it recognizes the extra free space, or shows you "locked" sectors of your HD. I like auslogic disk defrag.

 

Someone else could be using your computer as storage for their files which can happen if you have been compromised.

 

If you haven't installed your windows updates, but have downloaded them, Windows will hide that space from you, just like with restore points, as noted above. The page file could also just be flipping out because there's no space left.

 

Update: Enabling the "Wipe free space" option on CCleaner seems to have done the trick. 700+ MBs freed which brings the system back to within expectations.

Overnight virus scan revealed nothing unusual, so I guess that's my problem solved.