The technique of password grinding involves continually logging on remotely to machines, guessing a new password each time. This is usually difficult for hackers to do because most services are wise to this trick, and lock out the hacker after a 3 or 4 attempts in short period of time. Hackers can avoid this problem by trying different passwords very slowly.
Grinding works another way as well. Instead of trying one machine, the hacker can attempt to log onto many different machines with the same password. For example, the password "password" is very common, so a hacker might try logging onto all accounts using that password.
A hacker may also attempt to try different protocols so that no one service can lock them out. This is not always effective, as most systems come with central account system that all authentication must go through: it will lock out the hacker no matter what service he/she comes in on.
Not every system locks out hackers. Win95 and Win98 let somebody try an infinite number of combinations. Similarly, many Windows services (such as PCAnywhere) do not lock out accounts. This is because end-users frequently do not have "system administration" knowledge necessary to re-enable accounts.
Protocols:
