Conficker, also known as Downadup or Kido, was expected to wreak havoc on April 1 when it was due to be activated, but it failed to cause many problems.

Internet virus experts, however, claim it is now quietly turning thousands of personal computers into servers of e-mail spam and installing spyware.

The worm started spreading late last year, infecting millions of computers and turning them into "slaves" that respond to commands sent from a remote server that effectively ...