Security experts have admitted that the Conficker worm has baffled them.

The worm has infected more than five million computers in a botnet that is powerful enough to take out the internet in Australia, according to the Sydney Morning Herald.

Rodney Joffe, a director of the Conficker Working Group formed to defeat the worm, said, "The general agreement in the security world is that Conficker is the largest threat facing us from a cyber crime point of view. It has proven to be extremely resilient. It's almost impossible to remove."

The worm, which spreads rapidly among PCs by exploiting a flaw in Microsoft Windows, first surfaced last November.

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