Rainbow tables reduce the difficulty in brute force cracking a single password by creating a large pre-generated data set of hashes from nearly every possible password Rainbow Tables. This method, known as the Faster Time-Memory Trade-off Technique, is based on research by Martin Hellman & Ronald Rivest done in the early 1980's on the performance trade-offs between processing time and the memory needed for cryptanalysis. In this paper, the authors review some of the most important works in rainbow table generation and using rainbow tables in window NT environment, i.e. against NTLM. They will discuss how NTLM is weak against rainbow table attacks.