Google has pledged that it will not sue any open-source software projects for infringement of a selection of its impressively wide-ranging patents, and is encouraging others to do the same.

Software patents are an extremely divisive subject: those who hold them frequently claim that they are vital to encourage innovation, while those of a more open-source bent claim that they do the exact opposite. A software patent can be, and sadly often is, used to extort cash from the competition - or even to put them out of business entirely - should they come up with a similar process for achieving the same goal. Questionable software patent cases in recent memory include Microsoft co-founder Paul Allen suing a raft of companies regarding website functionality, the Discovery network suing Amazon over its digital distribution system, BackWeb suing Microsoft over BITS, and Implicit Networks suing pretty much every technology company under the sun.

The patent world has even generated its own business model, that of so-called 'intellectual property' companies who exist purely to purchase unused patents from other companies and then use them to force royalty payments and damages out of alleged infringers. Described as 'patent trolls' by those who oppose the concept of software patents, it's a lucrative business model for many including IP specialist Eolas which sued Microsoft for $512 million before setting its sites even wider.

Google has taken the first steps along the road to ensuring it cannot be accused of such behaviour, announcing that it will be exempting selected patents from its arsenal. While it will retain said patents, it has pledged that it will not use them against any open-source software projects that choose to make use of the technology, reserving them instead as defensive measures in case Google itself is sued.

Described as the Open Patent Non-Assertion (OPN) Pledge, the company's announcement means that open-source projects that bear a striking resemblance to technologies developed at Google can breathe a little easier. 'We pledge not to sue any user, distributor or developer of open-source software on specified patents, unless first attacked,' explained Duane Valz, Google's senior patent consultant, in a blog post on the matter. 'We hope the OPN Pledge will serve as a model for the industry, and we’re encouraging other patent holders to adopt the pledge or a similar initiative.'

Before getting too excited, however, there are limits to Google's largesse, chief among these being the number of patents covered by the pledge: far from extending to its many thousands of patents, so far the company has only announced 10 - all relating to MapReduce, the big-data processing system the company developed for its search database - with the remainder still open for use as lawsuit-fodder. The pledge also only covers open-source projects: if a company develops a closed-source product that could infringe one of the OPN patents, Google is still free to sue the company, its distributors and even its users if it so chooses.

Despite this, it's a clear step forward and includes some helpful measures that could give open-source projects a boost including a section that ensure that the OPN pledge is in force for the life of the patents even if Google sells said patents to a third party.

'Over time, we intend to expand the set of Google’s patents covered by the pledge to other technologies,' claimed Valz. 'We hope the OPN Pledge will provide a model for companies looking to put their own patents into the service of open-source software, which continues to enable amazing innovation.'