tl;dr:

The crypto component of Windows was discovered to have a 1024-bit public key embedded within it whose symbol name is _NSAKEY. The "obvious" assumption was that this permits the NSA to read, sign, or authenticate anything for Windows. Microsoft denies this and says that "we have not shared this key with the NSA or any other party".

I remember when this story first broke. I thought it would lead to major embarrassment and repercussions for Microsoft. Boy was I wrong. There was no news coverage; other than a small subset of techies, nobody was concerned; and as far as I know, Microsoft never gave a technical explanation of how it was intended to be used.

There was no news coverage because virtually no expert in the field believes it to have been an NSA backdoor. The arguments suggesting it is were debunked by Bruce Schneier more than a decade ago. Among them, the obvious: Microsoft held the other key, the "non-NSAKEY" key, and could do anything that the NSAKEY can do. If NSA can coerce Microsoft into adding a whole new signing key, it could just as easily have coerced Microsoft into signing things with Microsoft's own key. Given that, an "NSAKEY" backdoor is irrational.

In promoting the notion that "NSAKEY" is a backdoor, you're lining up against the likes of Bruce Schneier and lining up alongside the likes of WorldNetDaily, which is indeed among the top Google search results for [NSAKEY backdoor].