Microsoft's plan to get the Pentagon to dump its move to open source may have backfired.

Pentagon sources have confirmed that the Redmond giant has been contacting officials at the Defense Information Systems Agency and the office of defence secretary Donald Rumsfeld during the past few months.

Microsoft has apparently been telling them that open source software threatens security and its intellectual property.

But a report prepared by Mitre Corp for the Department of Defense (DoD) concluded that the open source program should be expanded.

The report said that banning open source would have "immediate broad and strongly negative impacts on the ability of many sensitive and security-focused DoD groups to protect themselves against cyber attacks".

Microsoft has confirmed that it has been talking to the Pentagon, but denied urging a ban on open source. A spokesman said that the company has been discussing how to allow open source and proprietary software to coexist.

But John Stenbit, an assistant secretary of defence, and chief information officer at the DoD, told Reuters that Microsoft claimed that using free software with commercial software might violate companies' intellectual property rights.

The software giant had complained that by funding research on open source the Pentagon is effectively subsidising Microsoft's competitors.

The Mitre report indicated that open source systems and tools were being used to run a web portal for the Defense Intelligence Agency and network security for the US Army in Europe.

Among the most high-profile efforts is research funded by the National Security Agency to develop a more secure version of the open source Linux operating system, which competes with Microsoft's Windows.