W32.Blaster.Worm exploits the DCOM RPC vulnerability. This is described in Microsoft Security Bulletin MS03-026, and a patch is available there. You must download and install the patch. In many cases, you will need to do this before continuing with the removal instructions. If you are not able to remove the infection or prevent re-infection using the following instructions, first download and install the patch.
Additional information, and an alternate site from which to download the Microsoft patch is available in the Microsoft article “What You Should Know About the Blaster Worm and Its Variants.”