Passwords are a killer ... sometimes member join other forums and use the same passwords from another. This looks like the case with your forum. If remembering passwords are a pain in the butt for some of you, here's a free program that I reccommnd to all of my members (RoBo Form):
http://fileforum.betanews.com/detail...fid=1014298205
Also, one of the guys in the Full Release Section created a very nice password changer hack that requires all members to change their passwords after a period you can define. You don't have to have all members change then, but you can make it a requrement for your staff to change their passwords.
For added saftey, it would be best to make it so that each password contains numbers and letters, and require that they are at least 6 characters.