Security experts have warned of a new mass mailer worm, W32/Netsky.b@MM, or Netsky.b.

Antivirus software vendor McAfee's Anti-Virus Emergency Response Team (Avert) said the worm is infecting PCs at a rate of 40 to 50 an hour.

A memory-resident mass mailer, the worm copies itself to folders on drives C: to Z:, including the words 'shared' or 'sharing', presumably to achieve peer-to-peer propagation.

After being executed, the worm emails itself out as an attachment with a randomly chosen file name.

Avert believes the worm may attempt to clean up the MyDoom backdoor by deleting the registry keys that load it at the system start-up.

The attachment may have a double extension, such as .rtf.pif, and may be contained in a .Zip file.

The email includes a variety of messages, including: 'I have your password!', 'about me', 'anything ok?' and 'do you?'.

Further information on the Netsky worm can be found here.