Antivirus companies are perplexed by a spate of recent viruses that contain messages in which the writers threaten to attack them.

Worm writers are threatening to attack antivirus companies F-Secure, Symantec, Trend Micro and McAfee. In the latest version of MyDoom--MyDoom.AE--the authors embedded a message ridiculing rival worm Netsky and promising to attack the antivirus companies.

The message has left antivirus companies unsure of what to expect.