First, stop the bug from running by hitting CTRL-ALT-DELETE and
bringing up the task manager. Look for msblast.exe in the list, and
kill it. Now your computer won't shut down, but the bug is still there
and will run the next time you start your machine. Go to this URL to
find out how to get rid of it: http://securityresponse.symantec.com/avcenter/venc/data/w32.blaster.worm.removal.tool.html
If you've connected the PC to the Internet without having first
enabling a firewall, without having first installed an antivirus
application with current virus definition files, and/or before
installing the KB824146 Hotfix, you're very likely to have been
infected from any of the thousands of PCs on the Internet that are
constantly broadcasting the Blaster and/or Welchia worms. It only
takes a few seconds of exposure.
To stay on-line long enough to get the necessary updates, patches,
and removal tools, click Start > Run, and enter "shutdown -a" when the
next RPC countdown begins. This will abort the shut down. Also, make
sure you've enabled a firewall before starting, to preclude any more
intrusions while getting the updates/patches/tools.