1. To continually guess passwords to find the correct one. Analogy: If someone steals your bank card, they cannot sit in front of the cash machine and guess all possible PIN numbers. After a certain number of unsuccessful tries, the bank machine will "eat" the card. Key point: Secure systems (UNIX, Windows NT) lock out accounts after a certain number of unsuccessful tries. These lock-outs can either be temporary (and restore themselves automatically), or permanent until an administrator intervene and unlocks the account. Key point: Non-secure systems (Win9x and many software applications) do not lock out accounts. For example, if you have Win9x "File and Print Sharing" turned on and protected with a password, a hacker can try continuously and invisibly to gain access to your machine. Nothing is logged, nothing is locked out. Contrast: When brute-force cracking, the hacker does all the calculations himself (comparing them against the stolen encrypted password file). When doing a grind, the hacker must enter the passwords one by one, and the target system does the calculations to see if they are valid. An intrusion detection system can detect grinds, but not cracks. From Hacking-Lexicon