According to Andrew Fernandes, Chief Security Scientist for Cryptonym, Microsoft placed an NSA backdoor in Windows 95/98/2K and NT.

The backdoor was discovered when Fernandes was investigating Microsoft's CryptoAPI architecture which underpins the cryptographic security architecture of Windows. Sloppy programming by Microsoft had left annotation identifying the security elements. The first public key belonged to Microsoft and the second belongs to the NSA. It was identified with the symbol _NSAKEY.

The backdoor could allow the US's National Security Agency to load unauthorised CryptoAPI applications on any computer with the Windows operating system.

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