Hello Guys,
sometime ago i have setup a nice Debian FTP server. and left the company. everything was working fine for about 5 month, administrator was able to login to root, do changes and manage system, etc. Suddenly he told me that he cannot login via PUTTY, the root user and pass say Access Denied.
Looked all over the web for at least a REASON, but did not find anything. I suggested to go and do passwd reset, via runLevel 1. i hope this helps him. But i am still curious why all of the sudden, in a locked down room, where only one person has access root get disabled.. Hacking?

Just a quick suggestion on my way past.. Did someone disallow root to login via SSH? Can root still log in at the machine its self?

I agree with Flyte, it sounds more like someone decided to implement a more sensible SSH policy. However, if root is lost at the machine itself, then you may have a more serious problem.

Thanks for ideas,
i only know that putty was not letting in, so ssh is not working, as far as physical login from console, no info on that, waiting...
but why would suddenly stop working? unless some one touched it, i will hit you up with some details, i think that reseting at runlevel1 should help.
but for personal knowledge would want to know.
i know that system was behind a sonic-wall firewall-router, probably with default security config and some ports forwarded

Just in case you're missing a subtle, but very important point, let me ask this....Is putty not working for any user or is putty not working just for root? Any well-managed box should not be allowing root login via ssh, so if root is the only account you're looking at it could be that SSH has been reconfigured so that root is not allowed, but other users are.

Actually if you have been compromised (and at this point that is pure speculation) you'd be better served not to mess with the runlevel (you want to preserve evidence), but rather simply disconnect network access. If you have physical access simply pull the network cable. If you're dependent on SSH, set up the firewall so that SSH is only allowed from trusted IP addresses.

There are lots of reasons why SSH might stop running so until you can figure it out a bit better, don't going doing things without a specific reason.