Anti-virus vendors today warned of the rapid spread of yet another mass mailing virus.

Bugbear-B, a variant of the infamous Bugbear, is a complex mass-mailing worm with a variety of nasty tricks up its sleeve. It spreads by either emailing itself to addresses found on infected PCs or (less commonly) via network shares.

As usual it's a Windows-only menace. Mac and Linux users are immune.

Like its predecessor, Bugbear-B can propagate using the MIME MS01-020 vulnerability and is particularly difficult to spot. This is because it normally arrives in email with variable subject, text and attachment names.

Since its discovery on Tuesday, Bugbear-B has reached near-epidemic proportions.

Bugbear-B utilizes numerous subject headers as explained in greater depth in an advisory by McAfee here.

The message body and attachment name vary as well and may contain fragments of files found on the victim's system.

If you're on a Windows system and open an infectious attachment, you get the pox.

Once activated Bugbear-B emails itself to addresses found on the local system using a user's default SMTP engine and spoofed (forged) email addresses.

Additionally, Bugbear-B contains a polymorphic parasitic file infector, which (translated into English) means the virus changes with each infection. It's the Mystique of malicious code.

The virus also tries to infect multiple files including mplayer.exe, notepad.exe, regedit.exe and winhelp.exe, amongst others.

Nasty.

As if that wasn't enough, the worm has keystroke-logging and backdoor capabilities and also attempts to terminate the processes of various anti-virus and firewall programs.

Symantec's advisory explains this pernicious behaviour in greater depth.

AV firms are unanimous is describing the virus as high risk.

Standard precautions apply to defending against the bug: update AV signature files and (if you're an admin) consider introducing controls to block executables at the gateway. If you're a regular user, be careful of those unsolicited attachments... ®

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