The European Commission (EC) has officially charged Microsoft for failing to provide the browser choice screen to users after a botched update removed the system from its Windows software.
The issue first came to light in July when it was revealed a Windows 7 Service Pack 1 update did not include the browser ballot choice screen.
This was a system Microsoft was meant to provide to all customers after a commitment made by the firm to the EC in 2009.
This commitment required the firm to offers users of its Windows system the use of alternative browser choices to its own Internet Explorer (IE) tool, such as Firefox, Chrome and Safari, until 2014.
However, the Service Pack update failed to include the ballot, meaning millions of customers were never presented with the choice of alternative systems.
"The EC has informed Microsoft of its preliminary view that Microsoft has failed to comply with its commitments to offer users a choice screen enabling them to easily choose their preferred web browser," it said in a statement.
The EC's statement doesn't pre-empt any decision on the case, but it has the right to fine firms a maximum of 10 percent of annual turnover. For Microsoft this could be as high as £7bn, although it seems unlikely the EC would impose such a high fine.
Microsoft apologised again for the mistake and said it had taken steps internally to ensure such an incident couldn't happen again.
"We take this matter very seriously and moved quickly to address this problem as soon as we became aware of it," it said.
"Although this was the result of a technical error, we take responsibility for what happened, and we are strengthening our internal procedures to help ensure something like this cannot happen again."
The incident comes as Microsoft prepares to officially launch its Windows 8 software on the market. This has also caused browser concerns with some rival firms concerned the classic Windows environment offered within Windows 8 will not run other browsers.
However, the EC has said it has received personal assurances from chief executive Steve Ballmer this will not be the case.
Elsewhere, the firm 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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