SOUTH African research into an Aids vaccine has received a boost from an unexpected source: the antivirus software used to detect spam in Hotmail.

Researchers at Microsoft are using spam-defeating software similar to that used by Hotmail - the world's largest web-based e-mail service - to search for the constantly mutating human immunodeficiency virus.

Like e-mail spam, which is constantly being adapted to evade the latest countermeasures, the many strains of HIV frequently mutate.

Antivirus software has been designed to detect the core details of spam - and this ability is being used against HIV.

The central research is being done at the University of KwaZulu-Natal's Centre for the Aids Programme of Research in South Africa (Caprisa) and the KwaZulu-Natal Research Institute for Tuberculosis and HIV.

The data is used by the Ragon Institute of the Massachusetts General Hospital, MIT and Harvard - with software help from thousands of computers at Microsoft Research in Seattle, US.

David Heckerman, who developed the computational biology software called PhyloD, said: "Before I was working on HIV I was working on spam filters. I actually invented the spam filter [for Hotmail].

"When it came to HIV, it was sort of the same thing. We had our immune systems like spam filters trying to block HIV; and HIV mutating to get around the immune system. So we had the same idea: let's go after the achilles heel of HIV."

In a telephone interview, Bruce Walker, Ragon Institute director and professor at Harvard Medical School, said: "What you have to do is teach the immune system to attack a virus at its most vulnerable positions.

"We believe the immune system is wasting a lot of ammo shooting at things that just don't matter to the virus. The virus is putting up decoys."

Walker is also an honorary professor of medicine at UKZN, where he works with Professor Thumbi Ndung'u, the director of the HIV pathogenesis programme at the university's school of medicine.

Professor Salim Abdool Karim, director of Caprisa, said "This high-end computing helps us understand mathematically how the body responds to the virus."

Although data-crunching using powerful computers is common in medical research, this is the first time antivirus software has been used.