Many website visitors often fill in many registration or login forms and there is often required a passwords. Have you ever tried to crack a password? It is quite easy for basic programmers. But all depends on how strong the password is. It means how many characters does it have or if the password contains some numbers or upper case letters. The more complicated password is, the harder is to crack it by someone. Very helpful tool for checking the strength of particular password directly in form is the Ajax Password Strength Meter.
Simply download JavaScript file, set some parameters and try. Runs in all modern browsers with JavaScript enabled.