It's not a worm.
http://www.symantec.com/avcenter/attack_sigs/o93.html 

Nmap is a network utility (standard on most *nix boxes) that can be used to identify open ports on a machine, and is often used by hackers to identify vulnerable ports.
It can also be used for the less sinister purpose of identifying the operating system of a connecting computer, although Windows operating systems don't respond to the scan in the standard manner. Probably not the wisest choice in this age of excessive paranoia.