Can't change user password

[Juan Bernhard]

Hello list, I have a really strange problem. I can't chage a user
password, I tryed from the user itself, from root, in sigle user mode...
I also try to change the hsash in /etc/master.passwd. The passwd command
exit successfully, but nothing happens, the old password is not changed.
The only solution I found is to delete the user and create him again...

I have 8 server with freebsd, whit the same user and password on them. I
found the same problem on the same user on 4 servers... Im afraid of
being hacked
This servers has this in common:
They are all virtual (vmware)
The user was created on the installation (this is the user that I use to
enter by ssh)
The user group is wheel
Their version is 8.4 and 8.3

I runned 'freebsd-update IDS' whit no interesting results. But if the
server is compromised, I think this command could be useless too

Any suggestions?