Security and login problems

Question

iMac G5, 10.3.9
Recently, the computer began to occasionally refuse passwords for accounts when trying to log on. From the logon screen, selecting an account and typing the password wouldn't work. The only solution was to restart.
Unfortunately, when re-started, the computer bypassed the login screen and went straight to the Admin user account, allowing any user access to all functions. This is a major security problem. (Note, once re-started, logging out and back in worked fine, with passwords correct for each account).
I ran Repair Permissions and thousands were fixed. Ran it again and it checked out fine. Now, restarting bypasses the login screen entirely, going straight to the Admin account. If you log out and back in, all still works fine.
This is a serious problem. What's going on and how can I fix this?
Carl
Powerbook Pismo (G3 400)   Mac OS X (10.3.9)  

Answer 1

Thanks, ali.
It is, in fact, set as automatically log in as the admin account. Odd because it was never set that way in the beginning, but this is a relative's computer, and maybe someone else re-set the auto log in. I've re-set it back and will test the system again.
Anyway, any ideas why the passwords would get corrupted and not work while the system is running? It typically happens when the computer goes to sleep.
Carl