Bagle the 13th spread defies belief

When will the madness end?

To nobody's great surprise, another Windows-infecting mass mailing worm began spreading over the Net last weekend.

Bagle-N is spreading rapidly and most anti-virus firms rate it as medium to high-level risk. Email filtering outfit MessageLabs has intercepted 11,105 copies of the worm since Saturday.

The worm normally spreads by email but it also capable of propagation across P2P file sharing networks. Bagle-N arrives in either a password-protected zip or rar file, and the password is either included in the body of the email, or in an image file attached to the email.

Apart from the image-file ploy (a minor 'innovation' in virus writing), Bagle is little different from its 13 predecessors - not least in the fact that it infects Windows PCs only.

Bagle-N commonly comes in email messages with variable subject and attachment names. The ‘from’ field of the email is spoofed so that it appears to come from a potential victim's sysadmin. Message bodies warn that the user's email account "might be disabled" or suffer some other odious consequence if a user fails to open an attachment.

If you open the worm's infectious archive file you may infect your PC. The worm disables many security software packages and includes a backdoor component which listens on TCP port 2556. Bagle-N scours the hard drives of infected computers for email addresses. It then sends copies of itself to these addresses using its own SMTP engine. It is programmed to stop spreading on 31 December 2005, so instead of being around for days this infector will likely to around for months.

As usual, users are warned to minimise risk of infection by not clicking on unknown attachments in emails. Updating anti-virus signature definitions is also a sensible step. ®

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