Window of exposure lets viruses run rampant

More than 295,000 virus-infected emails were sent to companies in the UK in May before anti-virus vendors could issue signature updates, according to email filtering firm BlackSpider Technologies. It’s long been known that there is a ‘window of exposure’ - the interval between when a virus begins spreading and signature updates are issued by anti-virus vendors. BlackSpider has put a figure on this phenomenon in order to back up its argument that there’s a high risk of infection during this ‘window of exposure’ for firms that rely on conventional anti-virus scanners alone.

Vendors that make most of their money from desktop or server-based anti-virus scanners argue that most of these viruses could be thwarted by a policy of blocking executable attachments in email. They also argue - with some justification - that many instances of virus infestation occur because people don’t keep anti-virus protection up to date and that older viruses pose the greater problem. Furthermore looking at virus-infected emails – rather than figures on virus-infected PCs that are harder to obtain – slews stats towards newer, chattier viruses. Desktop anti-virus protection also defends against viruses that propagate using browser exploits, unlike email filtering services.

"Blocking at the perimeter alone is dangerous because viruses can spread through variety of methods, such as IM and P2P, as well as email. Users need protection at the heart of their organisation," said Carole Theriault, a security consultant at Sophos.

Email filtering firms, such as BlackSpider and MessageLabs, counter-argue that their services are needed in addition to conventional anti-virus defences. The ability to recognise and quarantines viruses before patches are issued by anti-virus vendors helps corporate security, they argue. This approach also allows more aggressive filtering.

According to BlackSpider, the recent fast-spreading Sober-P virus proved particularly problematic for anti-virus vendors who took more than two days to issue signature updates that picked up all copies of the variant. The two most damaging virus outbreaks of last month occurred on May 31. MyTob-BC proved the most prolific, with approximately 69,500 emails being sent to UK businesses prior to the first signature updates being available from anti-virus vendors, while the Bagle-BO virus ran it a close second. Blackspider blocked 67,000 copies UK business email addresses before anti-virus vendors issued a signature update.

Spohos’s Theriault said that heuristic (automatic detection) features in its products picked up Bagle-BO without the need to issue additional anti-virus signatures. ®

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