If you receive MyDoom.s, do not open the attached file. The best way to prevent infection is to make sure that your antivirus signature files are current. Also, a personal firewall will prevent the virus author from gaining remote access to your PC.
A few antivirus software companies have updated their signature files to include this worm. This will stop the infection upon contact and in some cases will remove an active infection from your system. For more information, see Computer Associates, F-Secure, McAfee, Norman, Panda, Sophos, Symantec, and Trend Micro.