A newly discovered worm has begun spreading in the wild, sparking what security experts warn could be another slanging match between rival virus writers.

The Fatso.A worm (also known as Crog and Sumom) spreads via MSN Messenger by sending an instant message with a URL that, when clicked, causes the PC to download the virus. It also spreads as a file on eMule peer-to-peer systems.

It contains a message from a virus writer called 'Sky Devil': "Hey LARISSA f*** off, you f****** n00b!.. Bla bla to your f****** saving the world from Bropia, the world n33ds saving from you!"

The reference to Bropia is aimed at the author of the Assiral.A worm. Assiral.A is designed remove the Bropia worm and its variants from infected PCs, although it is not benign itself.

Assiral.A arrives as an email attachment in Outlook purporting to be a love letter. Once activated it removes Bropia but drops other worms onto the computer, including one that displays the following message on infected PCs: "LARISSA OwN'z U:-) Larrissa ~ V3rzi0n B Anti Bropia - Freeing the w0rld fr0m br0pia."

Both Bropia and Assiral.A have been detected in the wild in relatively low numbers. Fatso, however, appears to be gaining traction in the US and South Korea.

The conflict could be a repeat of the online slanging match that occurred between the MyDoom, Bagel and Netsky virus writers.