Windows: Many utilities, such as JkDefrag, jazz up their routine scans by presenting them as screensavers. Security Essentials Screensaver turns your computer idle time/screensaver activation into malware and virus scanning time.
The screensaver comes in two flavours, graphical and non-graphical. The graphical one displays the Microsoft Security Essentials logo and the non-graphic one simply blanks the screen like the default windows "Blank" screensaver. Scanning pauses when you return back to work.
For more ways to increase the usefulness of your screensaver make sure to check out how to use your screensaver as an instant away message, and keep an eye on world news via RSS feeds.
Microsoft Security Screensaver is freeware, Windows only.