In this variation of password cracking, we form password guesses based on parameter input rather than using a predefined dictionary. The objective here is to target one particular user, rather than the whole population, and attack that one user's password in an effective way. It started out as a "hacker's tool" that we developed for penetration studies, but it is also valuable to illustrate the importance of password selection and other security controls.
Guessing can be optimized based on what might be known about the password in general (length, number of vowels or numerics, etc.), or about any of the specific characters in it (e.g. the first character is 'Q', or the fifth character is a numeric, etc.).
How long does it take to crack a password? Check this out to get a feel for how PWCHECK-PRO might perform in your shop.
The PWCHECK-PRO documentation has a lot of detail on the brute force feature.