Nokia has put the full weight of its patent portfolio behind the Linux open source operating system.

In a legally binding document posted on its website Nokia pledged not to enforce any of its patents that are infringed by current official releases of the Linux kernel.

Patent litigation is considered one of the biggest threats to open source software development. A successful claim could initiate similar assertions to those made by SCO, a software developer that claims to own the copyrights for Unix and demands punitive damages and royalty payments from developers and end users.

Nokia's guarantee is limited to existing versions of the Linux kernel, and the company reserves the right to enforce patents against future versions and functionalities of the operating system.

The company promised to work with the open source community to identify such potentially infringing functionalities in advance.

Nokia is also working on broadening its pledge to other open source projects in which the company participates.

Giving Linux some weapons to fight back against patent claims, Nokia also vowed that it will go after parties that assert patents against the Linux kernel.

The phone maker's pledge follows an earlier promise by IBM that guaranteed the free use of 500 of its patents in open source software.

Sun Microsystems has promised to use a set of 1,670 patents to safeguard developers and users of the open source version of Solaris.