Microsoft is developing its own anti-virus software to combat the malicious programs plaguing users.
Microsoft's decision could be red rag to a bull for virus writers
The move will court controversy as traditionally Microsoft has stayed out of the anti-virus market, preferring to concentrate on its flagship Windows operating system.
Now it has announced plans to acquire Romanian firm GeCAD Software, and develop an own-brand anti-virus product.
Windows has long been a favourite target for viruses and any move to make anti-virus software could spur even more activity from malicious code writers.
"It could become like a red rag to a bull," said said Graham Cluley, senior technology consultant at anti-virus firm Sophos.
People think it is ironic that they could be getting fixes from the company that built the problems into the software in the first place
"There is already an obsession with Microsoft in the virus writing community and this could encourage people to write viruses to try and subvert it," he said.
Many of Mr Cluley's customers were surprised by Microsoft's decision to enter the anti-virus market, he said.
"People think it is ironic that they could be getting fixes from the company that built the problems into the software in the first place," he said.
In the mid-nineties Microsoft had a brief flirtation with an anti-virus product which it bundled with the Windows operating system.
"It was a disastrous flop and couldn't detect the viruses," said Mr Cluley.
There are no details about when Microsoft will release its new anti-virus product and the company has not yet decided whether it will be bundled with Windows.
If it is sold in this way, it could open the firm up to more accusations of acting anti-competitively.
It has announced that business customers will be able to subscribe to the service to keep their protection up to date.
Microsoft's shares rose 4% following the announcement while security companies Symantec and Network Associates both saw their shares fall.
Mr Cluley is confident that Microsoft's new direction will not signal the end for traditional anti-virus firms.
"To do anti-virus is quite a different discipline to producing other software," he said.
"Developers can spend time developing dancing paper clips but to combat viruses you have to be nimble and focused and the big challenge for Microsoft will be whether they can respond quickly enough," he said.
Microsoft currently bundles a firewall with the XP version of Windows but this has not stopped many consumers turning to protection products from other companies.