The European Commission (EC) has confirmed it has opened a new investigation into Microsoft to assess its compliance with the landmark 2009 browser ballot agreement.
Microsoft was forced to give users of its Windows operating system with a choice of browsers in order to ensure its own Internet Explorer (IE) tool is not given an unfair advantage against the likes of Firefox, Chrome and Opera.
However, the EC now said that a Windows 7 Service Pack 1 update rolled out in February 2011 may not have included the browser ballot system, meaning millions of users were not presented with the screen.
Compounding this, Microsoft claimed in its annual compliance report to the EC in December that it was fulfilling its obligations under the 2009 ruling.
"We take compliance with our decisions very seriously. And I trusted the company's reports were accurate," said Joaquín Almunia, vice president of the EC in charge of competition policy.
"But it seems that was not the case, so we have immediately taken action. If following our investigation, the infringement is confirmed, Microsoft should expect sanctions."
The EC has the power to impose a maximum fine of 10 per cent of a company's global revenues. In Microsoft's case, that would be worth $7bn. But it seems unlikely that the EC would seek to impose such a high penalty.
Microsoft admitted to the error in a statement, revealing it believes some 28 million PCs will have not received the Browser Choice Screen (BCS) system
"We have fallen short in our responsibility to do this. Due to a technical error, we missed delivering the BCS  software to PCs that came with the service pack 1 update to Windows 7," it added.
It also detailed the steps it has taken to address the problem, explaining it issued a fix within one day of the problem being discovered and has conducted outside investigators to uncover how the BCS system as missed from the update.
"Since we have fallen short in our responsibility to display the BCS, we have offered to extend the time during which we are obliged to do so by an additional 15 months," it said.
Microsoft already faces a fine of €860m after it refused to release code that could have been used to by other companies to create products compatible with its own was stifling innovation.
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