@matigo Back when banks and such were running Xenix or Unix and putting dial-up access for branches in, I used to dial in and find the OS default passwords.
Leave the admin mail to the effect of, "Dude, change your password".
They'd change it to something equally predictable sometimes.
Log back in and leave a mail that said, "Dude, change it to something else".
The late 80s were fun :)