Old minister helps beat spam

By ADAM GIFFORD

Praise the Lord and pass the plate. The mathematical theories of an 18th century Presbyterian minister are being pressed into service in the war on spam.

Thomas Bayes was the first to work out how to calculate, from the number of times an event has not occurred, the probability that it will occur in future trials.

Or, to put it more simply, P(H/E, C) = P(H/C) P(E/H, C) / P(E/C).

Companies trying to block unsolicited commercial emails or spam, but retain legitimate messages, are turning to Bayesian filtering, training the mailer by showing it a large number of junk emails as well as the sort of mail they want to get.

Many of these companies are start-ups, but the larger anti-virus vendors are also getting into the act, with Network Associates buying Deersoft and Trend Micro partnering with mail security service provider Postini.

Australasian channel and marketing director Greg Williams said by partnering rather than acquisition, Trend Micro's new subscription-based Spam Prevention Service was able to draw on the continuing intelligence about spam Postini achieved by processing 50 to 60 million messages a day.

More critically, Postini's technology throws up a very low percentage of false positives - Williams said some tests had come up with only one message in 90,000 wrongly blocked.

"Earlier filters used blacklists, which looked at the sender and said 'anything from this address is likely to be spam,' or whitelists of addresses to accept messages from.

"They also did things like looking at the subject line or the footprint of messages and compared them with lists of known spams.

"That created false positives - if I write 'love to see you next week' the message could be blocked, so someone has to go through the false positives and weed them out."

Postini calculates at least 70 per cent of email sent to corporates is now spam.

Williams said spam cost more than $20 million a year.

"Customers recognise it is a problem sapping a huge amount of productivity from organisations. People have to delete, delete, delete so time is being used up.

"There is also the issue about what it does to the bandwidth on a network, and you are storing this stuff so it is chewing up resources."

The Spam Prevention Service is aimed at large organisations and service providers and is available for Sun Solaris and Windows, with a Linux version due soon.

Trend Micro is also beefing up its New Zealand presence to cope with strong growth, appointing Damian Thompson country manager.