OIN chief executive Jerry Rosenthal told vnunet.com that Microsoft's assertions are simply an attempt to undermine the open source movement.
Rosenthal added that it is time for Microsoft to reveal the patents that are supposedly being infringed, or to drop the claims.
"The FUD is clear. If you have a patent that you are proud of, then disclose it," he said.
"If your patent is a good patent then you are not worried about revealing it before going to court because you would be confident of success."
Rosenthal believes that, if there are grounds for patent infringement, there would either be easy workarounds or the open source community would find 'prior art' which would invalidate the patent.
Rosenthal pledged to continue the work of the OIN as a protective measure until Microsoft stopped such tactics.
OIN buys patents on the open market and makes them available to companies royalty free, so long as those companies pledge never to use their own patents to attack open source code.
Mark Taylor, president of the Open Source Consortium, agreed with Rosenthal and described Microsoft's tactics in damning terms.
"We say show us the patents," he told vnunet.com. "This has been the strategy against open source all along. It's precisely the same tactics as SCO used: implied threats and mafia techniques. This is just FUD. It's smoke and mirrors. "
Taylor added that Microsoft is sorely mistaken if it hopes that its actions will slow down the spread of open source.
Laurant Lachal, open source research director at research firm Ovum, said: " Microsoft is too easy a bogeyman in this kind of situation.
"It is true that Microsoft is using FUD to attack open source, but the software industry has traditionally used FUD as a tactic. It is a normal way of doing business. IBM started it back when it was the powerhouse."
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