Companies should not fall for the temptations of purchasing a licence for Microsoft's intellectual property with their open source applications because it allows the software giant to "divide and conquer" the software market.

The comments were made by Eben Moglen, co-author of the forthcoming third version of the General Public Licence (GPL) and founder of the Software Freedom Law Center. 

Typifying open source applications as community software, Moglen argued that it requires a communal defence against patents from companies like Microsoft.

But Moglen told vnunet.com in a video interview that some in the community will be tempted to make a "private peace with the invader". 

"Divide-and-conquer strategies are built around the weakness that it is in the interest of some people to make a private deal for safety and abandon communal defence," Moglen said.

"We are trying to prevent a divide-and-conquer strategy from working. So it is important for us to say to people that they have to stick to the common defence.

"They cannot make private deals with the invader or the adversaries of the freedom of the software. We all have to stick together."

Microsoft and Novell unveiled a partnership in October that provides buyers of Novell's SuSE Linux operating system with a licence for Microsoft's patent portfolio, safeguarding them from intellectual property infringement claims.  

Contrary to common patent licensing agreements, the licence is granted to the individual user rather than to Novell. The deal met with harsh criticism from open source advocates including Moglen.  

Enterprises have been less critical about the partnership, however. Microsoft and Novell have signed several customers for their combined offering, and have published a survey which claims strong approval of the partnership.

Moglen recommended that Novell should engage in cross-licensing deals instead of providing patent licences to individual Novell customers.

But Microsoft does not want to engage in a cross-licence deal on Linux. The terms of the GPL require that a patent pledge to Novell is extended to all Linux distributions.

• A video of the full interview with Eben Moglen is available on vnunet TV