A few days ago, my computer got hit HARD by malware that included, among other things, a rootkit and DNS redirects. (It would eventually take more than a week to get rid of everything, and even now I'm a bit afraid to use it.) I normally keep my comp on 24/7, but after the malware it stayed off and silent. I have to say it was kind of freaky to come home late at night and NOT hear the humming of the computer.