SYSKEY was an optional feature added in Windows NT 4.0 SP3.

It was meant to protect against offline password cracking

attacks so that the SAM database would still be secure even if

someone had a copy of it. However, in December 1999, a

security team from BindView found

a security hole in SYSKEY which indicates that a certain form

of cryptoanalytic attack is possible offline. A

brute-force attack then appeared to be possible.