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Doug Krizner: The European Commission has opened a new anti-trust campaign against Microsoft. And as Megan Williams reports, the E.C. is responding to a familiar complaint.

Megan Williams: Just three months after Microsoft was forced to pay $800 million for breaking anti-trust rules in Europe, the computer giant is under the microscope again.

Two European software makers — ECIS and the Norwegian Opera — have accused Microsoft of blocking users from choosing rival software by keeping its file formats secret. They’ve also complained Microsoft unfairly ties the Explorer browser to its Windows operating system to shut out competitors.

The European Commission says that while the investigation has only just been launched, its victory against Microsoft last fall means it doesn’t have to prove certain practices give the company an unfair lead.

The investigation is expected to take at least two years.

I’m Megan Williams for Marketplace.