IT managers have slammed Microsoft's claims that Linux source code infringes on its intellectual property, and have criticized Novell's deal with the company saying it grants validity to the claims.

Microsoft CEO Steve Ballmer declared last month that Linux users owe the company intellectual property for using patented technologies, citing a 2004 report by insurance firm Open Source Risk Management that claimed the Linux kernel potentially infringes on 27 Microsoft patents.

Almost a month after Microsoft and Novell signed a partnership inhibiting the enforcement of patent and intellectual property rights until 2012, the latter paid Microsoft $US40 million in exchange for its pledge to not sue SUSE Linux customers and developers for what Ballmer coined an "undisclosed balance sheet".

Perth-based building firm BCG IT director, Andrew Buckeridge, said the claims are weak but will be a complication for open source developers.

"Microsoft's claims are not that strong, but this may cause fear, uncertainty and doubt for those who buy into it," Buckeridge said. "It may also cause major inconvenience and risk to free software developers who will have to get Microsoft's patents re-examined. I think that software patents, or patents bared on any kind of mathematical discovery, are very bad."

When asked about the implications of the ensuing Microsoft-Novell deal, Buckeridge said it gives credibility to the claims, comparing the situation to the intellectual property litigation between Microsoft and Unix vender SCO.

"The situation occurred with the payout between Microsoft and SCO, but I would expect the Microsoft-Novell payment to be much more than $US40 million in order to cause maximum fear, uncertainty and doubt," he said.

An IT support manager at a NSW university, who requested anonymity, said while the Novell-Microsoft deal was in the interest of its users and contributors it represents a "slap in the face" to fellow Linux proponents.

"Although I can see Novell acted defensively, it effectively bolstered Microsoft's ludicrous claims and created dangerous fodder for them to use in court," he said, adding that the deal could pressure other Linux users into paying fees to avoid litigation.

A somewhat philosophical Buckeridge said the claims arose because Microsoft has "paid too much attention to the opposition and not enough to the customer".

"One of best lessons I have learnt is to ignore the opposition and pay attention to customers, which is something Microsoft would benefit from," he said.

"Novell SUSE will slip behind the other Linux distributors because it is now tarred with the same brush as SCO OpenServer and UnixWare."