Microsoft on Monday said it would sell custom support agreements for legacy products, enabling companies in most cases to extend service contracts for as long as they need to.

The Redmond, Wash., software maker currently offers a two-year custom support agreement to companies that haven't been able to migrate to new products in the previous 10 years. The new offering provides the option of extending the custom agreement.

Microsoft, however, may not offer the service for some products, depending on whether there's enough customer demand. In addition, the extended service would only be available to subscribers of Microsoft's premier support packages.

"It there's customer demand, and its fiscally responsible for the customer and for Microsoft, then it could go on indefinitely," Greg Caldwell, spokesman for Microsoft enterprise services, said.

Microsoft decided to offer the additional support following a six-month review in which the company found that customers needed more time to migrate to new products or product upgrades, because of financial constraints or to meet regulatory requirements. Microsoft normally offers five years of mainstream support on all products, plus the option of a five-year extension.

"We felt it was a good decision to give customers more flexibility if they needed it, or wanted it," Caldwell said.

Under the custom agreements, companies would get the same services they currently receive, including security patches for vulnerabilities labeled as critical and important by the Microsoft Security Response Center.

In addition, subscribers would get access to the existing database of security and non-security fixes shipped during the mainstream support phase, and the option of requesting non-security fixes for new bugs at an additional fee.

Microsoft is charging a flat fee on a per seat basis for the extended service, but will negotiate separately with each company for a minimum and maximum number of seats, Caldwell said.