Anyone with a basic understanding of Windows security knows that Microsoft LAN Manager (also known as Lan Manager, LanMan, or LM for short) has a pretty significant security vulnerability with regard to authentication. LanMan uses a really weak method of hashing a user’s password. The resulting hash is know as the LM hash and the method of hashing is referred to as the LM hash algorithm. What was intended to be a one-way function, as hashing is, turned out to be crackable with a few hours of brute force attacks.
With today’s advancements in technology finding a hash is relatively simple for an amateur. Additionally, with all possible hash combinations having been precomputed and stored in a format known as rainbow tables, it takes a matter of seconds to recover the password from a hash.