Users and experts braced for Conficker action

Estimates of the infection rate vary from one million to 15 million. It has had three upgrades, each tougher than the last. It is highly sophisticated — and it is poised for action, as millions of copies of Conficker are set to contact the worm's creators for further instructions on 1 April.

But nobody knows what the Conficker worm will actually do on that date — if, in fact, it does anything.