As part of its investigation into Microsoft's failure to properly offer a browser selection screen to Windows users in the EU, antitrust regulators have announced that they are examining whether Windows 8 prevents the installation and use of third-party browsers.

Microsoft agreed to offer users a choice of browsers as part of its agreement with the European Commission three years ago. However, the browser ballot was not properly offered to users of Windows 7 Service Pack 1, provoking the EC to investigate Microsoft's compliance with its settlement agreement. As part of that investigation, the EC is looking into allegations that Microsoft does not provide third-party browser developers access to the same set of APIs as Internet Explorer has.

The regulator will also examine claims that Microsoft will not allow any third-party browsers at all on its Windows RT operating system that runs on ARM processors, according to EC spokesman Antoine Colombani. The EC did not say which companies had made the allegations against Microsoft.

Windows 8 will support regular desktop browsers, which have full access to the system's APIs. It will also include support for Metro-style, touch-friendly browsers. These browsers have to comply with special rules, and only the default browser can offer a Metro-style interface (non-default browsers are relegated to the desktop).

Microsoft has not offered a corresponding set of rules for its Windows RT operating system.

Mozilla, creator of the Firefox browser, has voiced its concerns over the lack of access to Windows RT. However, Windows RT is not unique in this regard; neither Apple's iOS nor Google's Chrome OS offers the ability to install third-party browsers, nor will Mozilla's Firefox OS.