You may have heard a lot on the news recently about the Confiker virus/worm that is due to 'strike' on April Fools Day, tomorrow. A couple of simple steps could help prevent this.
First, be sure your systems are up to date. Look in the lower right hand corner of your Windows screen, near where the time is displayed. If you see a yellow shield, hover your mouse cursor over it. It may say that updates are waiting to be installed. If so, click on it and install the updates. It is most always a good idea to install these when they are available as they are designed to stop known threats. If you do not see the shield, go to Start -> All Programs and select Windows Update, usually near the top of the list. Follow the instructions to install all critical updates. Do this on all of your workstations and servers.
Second, check to see if you are already infected. The Confiker worm blocks a couple of web sites it doesn't want you to access because they give information about combating it. If you can go to http://www.symantec.com/norton/theme.jspthemeid=conficker_worm&inid=us_ghp_link_conficker_worm and http://www.mcafee.com you likely aren't infected. While you're on the sites, you might want to read up a bit on Confiker.
If a Conficker infection is suspected, the infected system should be removed from the network. Major anti-virus vendors and Microsoft have released several free tools that can verify the presence of a Conficker infection and remove the worm. Instructions for manually removing a Conficker infection from a system have been published by Microsoft in http://support.microsoft.com/kb/962007.
Source: US-CERT Technical Cyber Security Alert TA09-088A -- Conficker Worm Targets Microsoft Windows Systems