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LONDON, England (CNN) -- A new sleeper virus that could allow hackers to steal financial and personal information has now spread to more than eight million computers in what industry analysts say is one of the most serious infections they have ever seen. Experts say a single infected laptop could expose an entire network to the worm.

The Downadup or Conficker worm exploits a bug in Microsoft Windows to infect mainly corporate networks, where -- although it has yet to cause any harm -- it potentially exposes infected PCs to hijack. Mikko Hypponen, chief research officer at anti-virus firm F-Secure, says while the purpose of the worm is unclear, its unique "phone home" design, linking back to its point of origin, means it can receive further orders to wreak havoc.

He said his company had reverse-engineered its program, which they suspected of originating in Ukraine, and is using the call-back mechanism to monitor an exponential infection rate, despite Microsoft's issuing of a patch to fix the bug.

"On Tuesday there were 2.5 million, on Wednesday 3.5 million and today [Friday], eight million," he told CNN. "It's getting worse, not better."

Hypponen explained to CNN the dangers that Downadup poses, who is most at risk and what can be done to stop its spread.

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