Hard drive free space kept changing.

About a week ago my hard drives free space was about 17 gb, I thought oh crap and started uninstalling stuff, I didn't think I had installed enough to make it that size. Anyway it was about 34gb after uninstalling but I was sure it was bigger than that before I started installing the things I had just uninstalled and I had even unistalled a big thing that had been on their a while before. So I started using the system maintainance thing and it went up to 46gb or so which was more what I expected it to be but it kept getting smaller over time and was back down into the 30gb area, so I checked which programs were active on my laptop and uninstalled a load of those I've ran Nortons system clean up tools as well. Anyway after all that it went up to 53gb, and again went down. After that deep defrag the other day it does appear to have become a more stable 54gb's.

I was a bit concerned that some virus was downloading stuff onto my laptop, hopefully its sorted now it was making me a bit nervous with the speed that it was going down at.