Rainbow Crack

Here's a GIAC GCIH (Sans GIAC Incident Handler) paper, submitted by Mike Mahurin, which describes the Microsoft LANMAN password decryptor, Rainbow Crack.

This tools uses a time-memory trade-off instead of brute force attacks on passwords. In other words, it can pre-compute the the resulting hash because the same user and password on different machines (using LM authentication) produces the same hash. This is the reason that, if possible, you should use more modern authentication or alternative methods for Windows authenticaion.