Microsoft has started selling its OneCare security software in the US at a fee of $49.95 for up to three computers. 

Consumers should be able to find better deals, as retailers are expected to offer special promotions and rebates.

Microsoft is also talking to computer manufacturers to have the software bundled with new systems, but declined to offer any details about future partnerships.

OneCare offers antivirus, system optimisation and backup software. Although media reports have focused mainly on the antivirus aspect, the other two features are equally important, according to Dennis Bonsall, director of Windows Live OneCare.

"I am trying to help consumers understand that OneCare is much more than [anti-virus]," he told vnunet.com. 

Backup services are becoming ever more important, Bonsall cautioned, as consumers use their computers to store digital photos and music from online stores.

"Consumers are tying up an awful lot of their memories and their fun on a PC that they are not protecting," he said.

Bonsall claimed that only 10 per cent of PC users back up their data. This rate jumped to 80 per cent for early testers of the OneCare service.

He likened OneCare to the pit crew at a race track that allows the driver to focus on driving and leave the vehicle's performance to the experts.

OneCare is limited to the US for now. Microsoft intends to start beta programmes in different geographies within the next 12 months, but Bonsall declined to provide any further details.

Industry analysts expect Microsoft's entry into the security market to bring down prices. Gartner has predicted that Microsoft will cause prices for antivirus suites to drop by 10 per cent per year. 

Others have argued that Microsoft will have a limited market impact because its competitors have a 10-year head start and a subsequent technological advantage.

Microsoft countered this criticism last week when the software received certifications from ICSA Labs and West Coast Labs, two independent security testing bodies.