The US National Security Agency (NSA) has been mired in controversy pretty-much whenever they have chosen to enter the 'public security' space.  Just think back to the Clipper encryption chip 'incident' from 1993.  Later there was the supposed back-door in Windows XP which simply turned out to be a non-event.

This time, it started all over again when the NSA's information assurance director Richard Schaeffer, told the Senate's Subcommittee on Terrorism and Homeland Security early last week that the agency had partnered with the developer during the creation of Windows 7 "to enhance Microsoft's operating system security guide."  Well, of course everyone with an opinion to share decided that Schaeffer MUST be talking code for 'backdoor.'

In reaction, a Microsoft spokesperson said "Microsoft has not and will not put backdoors into Windows.  The work being discussed here is purely in conjunction with our Security Compliance Management Toolkit."

Of course Microsoft would deny this; true or not!  What else would they say?

However, security researchers were generally in agreement with Microsoft on this one.  For instance, AVG Technologies' Roger Thompson (the chief research officer), noted earlier "I can't imagine NSA and Microsoft would do anything deliberate, because the repercussions would be enormous if they got caught."

Other commentators have taken similar views. 

The problem here is that The NSA has two very different roles and the exercising of one of them seems to trigger visions of the other.  Firstly, they are active (nay, VERY active) in SIGINT (Signals Intelligence), which in plain English means they spy on anyone they think needs spying on.  This role involves tapping pretty-well every communications system within reach and searching for items of interest.  Such searching obviously involves massive computer decryption hardware; hence everyone's concern.

The other role is COMPUSEC (Computer Security, sometimes now referred to as Cyber Security).  In this role, The NSA attempts to assist computer system developers to harden their systems against attack.  This is the role that triggered the 'backdoor' slanging match.

Overall, it would seem incredibly unlikely that such a backdoor exists.  Modern analysis techniques would expose it relatively quickly, especially now that so many people are actively looking for it!  The price that Microsoft would pay for such a discovery would be far too horrible for the company to even contemplate.