Conficker seems to spread more easily than previous computer viruses. It may be embedded in other software. If it happens to get into software you have stored on a so-called thumb drive -- the small memory devices you can plug into a computer's USB ports -- it contains code to activate automatically when it senses that the thumb drive has been plugged in.
Microsoft is worried enough that it has offered a $250,000 reward for information leading to the arrest of Conficker's creators. And ICANN, the international organization that hands out addresses on the World Wide Web, has gotten a dozen universities and computer-security organizations together to stamp out the bug. They refer to themselves informally as the Conficker Cabal.
"The important thing to recognize is how much better things have gotten in this space," said IOActive's Kaminsky. In 2003, he said, worms took down entire networks. But, in 2009, we won't see that, he said.
"Infection rates are much lower than they would have been if this had happened in 2003," Kaminsky said.
Computer scientists said most people probably won't notice anything wrong with their machines, even on April 1, if indeed some command is sent by Conficker on that day.
But for safety, Microsoft and other companies are working on a Web site as a go-to place for people who find their anti-virus software has been disabled by the worm. In the meantime, Microsoft has created a software "patch" that people can find HERE if it was not installed in their computers already.
Another useful site set up by Microsoft is called safety.live.com; find it HERE.
Furst said security people are "both afraid and sanguine." They believe they have good protections in place -- but they are not sure what they're up against.
"This one's pretty cutting-edge," he said. "The bad guys are ahead of the good guys."
Ki Mae Heussner contributed reporting for this story.