Security researchers warned of a new worm, called "Funner", targeting Microsoft's MSN Messenger instant messaging system.
The worm propagates by sending a copy of itself, disguised as "funny.exe", to contacts found through MSN Messenger.
The worm then makes registry modifications and overwrites entries in the Hosts file, a list used to map IP (Internet Protocol) addresses to websites. Only certain Windows systems, including Windows XP, are vulnerable, according to security researchers.
Researchers currently grade Funner a low threat because of light distribution, although Trend Micro rates its damage and distribution potential as "high".
Computer Associates International grades Funner's destructiveness as "medium", while Symantec reports fewer than 50 known infections, so far.
All three suppliers have removal instructions posted in security alerts on their websites.
Stacy Cowley writes for IDG News Service