Microsoft plans to release the product in early June.
Called Windows OneCare Live, the subscription service will compete with security products made by traditional Microsoft partners, including Symantec Corp. and McAfee Inc. — although the software giant insists that its aim is not to run those companies out of business.
Ryan Hamlin, general manager of Microsoft's Technology Care and Safety Group, said Microsoft is less concerned with converting people already using other products.
Instead, Hamlin says Microsoft's goal is to provide protection for users who don't have any added or up-to-date security — a group that Microsoft estimates comprises 70 percent of consumer users.
"There's plenty of room here, kind of, for all of us," Hamlin said.
OneCare, which is already available for free in test form, aims to protect people running the most recent version of Windows against Internet attacks and intrusive spyware.
It also promises to provide regular tuneups to help keep computers running smoothly, and offers users a way to back up and restore data.
The system will automatically update with the latest protections and occasionally add new features, Hamlin said.
Microsoft, whose Windows operating system and Internet Explorer browser are constant targets of worms, viruses and other disruptive attacks, announced more than a year ago that it would offer the paid service.
Hamlin said nearly 200,000 people are already trying it out. Anyone who signs up for the test by April 30 can buy the paid service for just $19.95 per year.
The subscription fee is for up to three personal computers. The service will initially be available only in English, although Hamlin said the company expects to launch test versions elsewhere in the world over the 12 months.
Shares of Microsoft fell 23 cents to $26.94 in afternoon trading on the Nasdaq Stock Market.