The decision to pull Windows XP from the retail market last year could result in another regulatory run-in for Microsoft, as it may have violated Russia's anti-monopoly laws.

Microsoft will face a hearing on 24 July, Russia's Federal Antimonopoly Service said in a news release. The FAS contends Microsoft may have violated its Federal Law on Protection of Competition.

After an investigation, the FAS concluded there still is demand for OEM (original equipment manufacturer) and boxed versions of XP, which Microsoft took off the retail market on 30 June, 2008.

Microsoft charges different rates for the same version of XP, and the company has also worked to reduce supplies of new computers with Windows XP, the FAS said.

"This contains elements of anti-monopoly violations, in terms of economically, technologically and otherwise unjustified fixing of different prices (rates) for the same goods," the FAS said.

Microsoft said it had not been notified of an investigation. "However, we will co-operate with any inquiry and remain committed to full compliance with Russian law," according to a statement.

Windows XP first debuted in 2001 and is still widely used despite the company's attempts to get people to upgrade to Windows Vista, which was released to consumers in 2007. In response, Microsoft allowed those who bought the Vista Business and Vista Ultimate editions to downgrade to XP.

Microsoft said in April it will allow OEMs that make netbooks to install Windows XP for one year after Windows 7 is available. Microsoft is set to release Windows 7 on 22 October.

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