A spokesman for the European Commission's antitrust agency has confirmed that the Commission is investigating browser choice issues on Windows RT and detailed more possible charges. Antoine Colombani told Computerworld that "we will indeed look at these allegations made by third parties in the context of the investigation opened yesterday on Microsoft's compliance with our December 2009 decision." These allegations were primarily made by Mozilla, which has complained that Microsoft's tablet-focused Windows RT operating system only allows third-party browsers in the Metro environment, not the more traditional Classic mode. It's also alleged that users may find it difficult to change the default browser.

As Colombani said, the investigation will proceed in conjunction with a separate probe over whether Microsoft followed rules put in place back in 2009, after it was found to be abusing its market dominance with Internet Explorer. Besides examining whether Microsoft is locking browsers out of Windows RT technically, Colombani confirmed the Commission would also look at two other allegations. The first claims that Windows RT does not show the browser choice screen Microsoft agreed to display as part of the 2009 agreement.

The second deals with another part of that pact. "Third parties allege that Microsoft is acting in violation of the browser commitments," Colombani said, "by discouraging computer manufacturers (OEMs) by means of payments or withholding payments under marketing programmes from setting third-party browsers as default in Windows 8." Since Microsoft is barred from setting browser requirements or retaliating against manufacturers who use third-party browsers, this allegation could mean Microsoft is doing more than simply favoring Internet Explorer in its software.