The Conficker Worm is set to do something tomorrow on April 1st. The Conficker.C worm is a serious threat that has triggered the security community to form the Conficker Working Group.
Researcher Felix Leder and Tillmann Werner from the Werner Honeynet Project published a last minute white paper titled Know Your Enemy: Containing Conficker.

They found a new way to detect the Conficker Worm on computers remotely. Tools for administrators are available now to scan their networks for infected computers.
Conficker changes apparently how Windows appears on the network. The scanning tools available now are using this effect to indentify infected systems. The tool is being integrated into most vulnerability scanning tools, including Tenable Nessus, McAfee, nCircle and the widely popular open source nMap.
More details on the Honeynet site, Conficker Working Group site. Via this press-release.

To protect your own PC for the April 1st action of the Conficker Worm make sure that your anti-virus software is up to date.