There are programs (and they are easy to write) which will crack passwords that are based on the above.
The ACTlab Rules of Use clearly state:
8. Do not let anyone know your ACTlab password(s).
Giving someone else your password -- including trusted friends, or even UT/ACTlab staff members -- is like giving them a signed blank check, or your charge card. You should never do this, even to ``lend'' your account to them temporarily. This is especially important now that you can view certain private information online (e.g., academic records through the Student Information Services program).
Your ACTlab username identifies you to the ACTlab user community -- anyone who has your ACTlab password can use your account and whatever they may do that affects the system will be traced back to your username; if your username is used in an abusive manner, you can be held responsible.
Furthermore, there is never any reason to tell anyone your password: every UT student and faculty member who wants an account of their own can have one; and if your goal is permitting other users to read or write some of your files, there are always ways of doing this without giving away your password.