The Conficker worm is now in its third mutation, known as "Conficker-C."
The virus has infected millions of PCs and for months, experts have been warning people to protect their computers because the worm was set to take a nasty turn Wednesday.
The world began watching the Internet more closely at midnight, looking to see exactly what Conficker would do.
"This virus is like a sleeper cell in the sense that it breaks into innocent people's computers and just waits there until it's given a command to wake up and do something harmful," explained Mark Rasch of the U.S. Department of Justice Crimes Unit.
People could have the virus without knowing it, but the huge computer screen in the war room of the cyber security firm Symantech shows the scale of the problem for Microsoft users.
CBN's IT Security Manager Josh Doak says the best protection is to check online regularly for Windows updates and keep antivirus software up to date.
If you can't, there is a good chance you have the virus.
"It will disable the automatic updates in Windows if you have it enabled, so you will find yourself missing patches," Doak explained.
He added that you'll no longer be able to get to security software sites like Symantech.com, Trend.com and Microsoft.com.
Conflicker is malicious software which allows a hacker to steal information and secretly control an army of computers.
But Doak says that control is not the hackers' only motivation.
"Someone wants to make money. You are not infecting 15 million computers just to delete files. You want to use it for something more than that," he said.
The FBI and Homeland Security are still monitoring the computer threat, but for the most part the virus' damage, Wednesday, seemed minimal.
Still, experts say that does not mean the worst is over.