Much has been communicated online about the Conficker worm. It affects Windows operating systems and takes advantage of serious vulnerabilities. Users who practice sound security practices have nothing to fear, although it is generally thought that infected machines will be particularly affected on April 1, 2009.
eWeek magazine has a useful article on Conficker.
Microsoft has published instructions on how users can protect themselves from the Conficker worm. Microsoft has also prepared an image describing the worm: