My Passwords are changing automatically!

["David Pratt" <david pratt firstserv co uk>]

Hi,
I seem to have a problem with my RedHat 6.0 box. Only I have root access and
there is only one user added (for telnet login).
Today, I was unable to login remotely using my user account. After
physically going to the server, I found that the root password was not being
recognised either.
I tried several re-boots, but no joy.
I finally got into the box by doing a linux 1 at lilo, then changed the root
password.

However, I am really worried now as to why this happened and how I can stop
it again in the future.

Does anyone have any idea as to why the password was not recognised? Is it
hardware, a hacker/cracker? I did not change any system passwords in the
last month and am running Apache, DNS and qmail.

Many thanks for any help
David Pratt