Since Friday, e-mail filtering vendor MessageLabs has intercepted at least 13,717 copies of the worm, dubbed Breatel.A-mm, and has issued a medium-level warning.
The worm travels as an e-mail attachment, under the subject lines: "Message could not be delivered", "Error", or "Mail Delivery System".
If the attached file is opened, the computer connects to a botnet -- a network of thousands of hacker-controlled computers used for illegal activity -- and begins to send data to the Symantec Web site in the hope of crashing it.
According to antivirus company F-Secure, the worm attachment contains a message to Symantec that says: "easy to talk but hard to work :) what about working in symantec? :P it is not only a mass mail worm it is also a lsass worm :)"
A Symantec spokesman said that the company's infrastructure was built to withstand such attacks.
The first copy of the worm was sent from Northern Ireland, MessageLabs said.
Silicon.com's Dan Ilett reported from London. For more coverage from Silicon.com, click here.
