What was the most destructive & infamous worm, virus, or other form of malware?

[Megamantn]

In the wake of the recent Facebook Fan Check virus, Koobface emerging on other social network sites & some people still infected with Conficker which wasn't a bad as feared, I ask you what you think the worst computer virus was to this day?

It could be a recent virus or a historical virus like MyDoom, Blaster, Michelangelo, Melissa worm or ILOVEYOU.

No, Fake viruses don't count so don't mention the Goodtimes virus or Bin Laden virus from MonkeyDOO.