Blaster appears to be doing some damage to the Internet as well as many corporate networks. And the payload hasn't even been activated yet...
http://www.nwfusion.com/news/2003/0812blastinfect.html
The Blaster virus (also known as LovSan or MSBlast) takes advantage of the newest advertised RPC exploit:
http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS03-026.asp
I almost never advocate installing a hotfix, but in this case the problems associated with the exploit attempts far outweigh any potential problems with the patch. Even if your machine is not infected, another infected machine can crash your RPC service thus disabling a lot of functions your programs rely on.
Try and get that patch installed as soon as possible, because when August 16th comes around the corner, windowsupdate.com won't be available as the payload is activated.