Rival security experts are urging Symantec users to update anti-virus software to combat a new variant of the worm known as either Rinbot or Delbot.

The worm exploits a vulnerability in Symantec software and seeks to set up botnets from which denial-of-service attacks can be launched. It propagates by creating emails with the worm program attached or by attaching the program to outgoing email, says Ron O'Brien, a senior security analyst at Sophos .

Symantec has the worm listed as one of two latest threats today, and has issued a Daily LiveUpdate that protects against what the company calls W32.Rinbot.L. Sophos calls the worm W32/Delbot-L.

The worm takes advantage of weak passwords to install on machines including Microsoft SQL servers using Windows network APIs, such as the Messaging API, says O'Brien. The worm creates registry changes in machines it infects that must be removed. Symantec classifies removal as easy.

The worm was detected at work against servers in CNN's network Wednesday, according to O'Brien.