from symantec website:
W32.Blaster.Worm is a worm that exploits the DCOM RPC vulnerability (described in Microsoft Security Bulletin MS03-026) using TCP port 135. This worm attempts to download and run the Msblast.exe file.
Block access to TCP port 4444 at the firewall level, and then block the following ports, if they do not use the applications listed:
TCP Port 135, "DCOM RPC"
UDP Port 69, "TFTP"
The worm also attempts to perform a Denial of Service (DoS) on Windows Update. This is an attempt to prevent you from applying a patch on your computer against the DCOM RPC vulnerability.
[center]People are Tricky you can't Afford to Show anything Risky..
Seeing is Believing. Feeling is Deceiving. I could be anyone but your friend..
I'm going out, I'm going to drink myself to death
And in the crowd I see you with someone else
I brace myself 'cause I know it's going to hurt
But I like to think at least things can't get any worse