A Spanish group that represents open source software users has accused Microsoft of using an "obstruction mechanism" to prevent buyers of Windows 8 computers from installing Linux-based operating systems.

That mechanism, of course, is UEFI Secure Boot, which improves boot-time security on machines designed to run Windows 8 by only booting operating systems signed with a trusted certificate. This requirement led to much consternation among Linux users in the months prior to the Windows 8 launch, but in practice probably hasn't prevented that many people from using Linux. UEFI Secure Boot can be disabled in a computer's firmware settings. Additionally, the Linux Foundation and others have provided workarounds that let Linux-based operating systems boot without disabling the security mechanism.

The 8,000-member Spanish open source group, Hispalinux, said in a complaint filed today with the European Commission that UEFI Secure Boot is "a de facto technological jail for computer booting systems... making Microsoft's Windows platform less neutral than ever," Reuters reported today. Users must obtain digital keys from Microsoft to install non-Windows operating systems, the group noted.

The EU this month fined Microsoft €561 million (or $732 million) for failing to comply with a previous antitrust agreement that required the company to provide Windows users with a choice of Web browsers. There's no indication yet of whether the EU will act on the UEFI complaint, however. Microsoft and European officials have not yet commented.

The fact that the EU hasn't already targeted Microsoft over UEFI Secure Boot may be good news for the maker of Windows. EU antitrust officials previously looked at how Windows RT, the ARM-based version of Windows 8, prevents the operation of rival browsers and decided that no disciplinary action was warranted.