Similar to a virus, a worm is a self-replicating program that does not necessarily alter files, but resides in active memory and duplicates itself. Worms use parts of the operating system that are usually invisible to the user. It is not uncommon for worms to go unnoticed until their replication eats up system resources, slowing or stopping other tasks.
The recent MSBlaster worm presented users with a myriad of problems including:
Additionally, the worm had the ability to launch an attack against windowsupdate.com. If all of the infected computers had tried to repeatedly connect to the site as planned, a denial-of-service would have resulted from all of the traffic (too many computers connecting all at once, resulting in the site becoming inaccessable). Microsoft's update site is NOT at that address, but they had an automatic redirection to the correct page from there. Fortunately, Microsoft found out about the potential attack and took down the windowsupdate.com redirection before the attack was to have started.
If people had been keeping up with their Windows Updates, the Blaster worm would have been a lot less damaging. The security hole that the Blaster worm exploited had a patch available almost 2 months before the worm hit the Internet!
