Ubuntu :: Secure Overwrite Of A Partition?

i have a duel boot of windows and ubuntu, but recently i got a virus, but this things is leach like in appearance. I tried reinstalling windows, then reformatting the drive and reinstalling windows but i still have this same virus? This is dead creepy for me because windows cant read any of the other partitions, which are all formatted for linux, in formats which windows does not have the capability to read. So i dont understand how this could have happened. There are many things that i am still to try -- including completely overwriting the MBR with a GRUB in case the virus somehow resides in there?? But i have decided to give up on windows from now, because, despite all the actions i have taken, it has failed me repeatedly. But having had these viruses 3 times, i have noticed something, the first time i had a virus was my fault, because i left my computer insecure.

After i formatted my HDD following that virus, i noticed i had 10gb of space robbed from me, disk utility believed i had a 160gb drive, but Gparted and everything else told me that i only had 149.7gb of space??? now after this virus - which logically couldn't have happened without someone directly attempting to tunnel my computer as i had so much extra security - i lost 6gb of space from my HDD?? Sounds odd?

THE QUERY: So i want to know if (from ubuntu) it is possible to do a secure format (similar to with a mac - were it completely overwrites everything, instead of just deleting the links) although, possibly i am not going back to windows, ever.