Bounced messages from auto-responders in receipt of the prolific Sobig-F worm are feeding a flood of useless and malicious messages that threatens to swamp legitimate emails for many users.
Sobig-F, like viruses such as Bugbear, Fizzer, Mimail and Klez before it, spoofs or forges the name in the From: field in infected emails sent out from pox-ridden PCs. This forged email address is often randomly plucked off the infected computer by the virus.
Some gateway applications that scan email attachments for viral content email auto-replies when a virus is found. If the 'Sender' name has been forged, the auto-reply can be received by an innocent party, causing undue confusion and stress. A false accusation may even harm an organisation's relationship with clients and partners.
Although we've seen the spoofed email tactic before, the explosive growth of Sobig-F is making the behaviour a greater problem.
Graham Cluley, senior technology consultant for Sophos Anti-Virus, said that the current generation of anti-virus gateway products are incapable of determining the email address in a virus contaminated email are spoofed.
"In the circumstances, it might be better for people to turn off their auto-responder," Cluley advised, adding the auto responder messages could be taken of an accusation that someone wholly innocent was sending out viruses.
"Sobig-F is causing problems for companies even if they're protected by clogging up email," he added.
According to managed services firm MessageLabs, the ratio of viruses to email has reached one in 28 - the same level reached at the height of the Love Bug epidemic.
MessageLabs technicians report that it has blocked over one million contaminated emails since the start of the Sobig-F epidemic. If anything the worm is growing in prevalence as time goes on, they report.
That suggests a very uncomfortable outlook ahead until Sobig-F reaches its built-in obsolescence date on 10 September.
Spam tools used to give Sobig-F a kick start?
So why has Sobig-F spread so fast, so quickly?
Sophos' Cluley theorises that the worm may have been given a "kick start" via the use of spamming technology. However, as Cluley himself says, this is a theory built only on circumstantial evidence.
Some have speculated that the combined effect of Blaster and Sobig-F might have a beneficial effect in forcing people to take anti-virus security more seriously. It's a nice idea but we're sceptical - as is Cluley.
"There may be some short-term benefit. But history shows that after every big virus there's a lull but then it all kicks off again," Cluley told us. "If any good comes out of this it might be to force a cultural shift among organisation forcing them to realise that there's really go good reason for them to receive executables from outside their organisation."
Cluley also hopes people will begin to see security as a community effort.
"Home users need to protect their systems if they don't want to behave like Typhoid Mary," he added. ®
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