IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
You get the above message when running ssh.
The issue is, you have connected to this host/ip in the past and the machine you are connecting to has been replaced and/or lots of updates have been done to it. If you know that this has happened, execute
ssh-keygen -R (host name or IP address)
and it will be cleared from the ~/.ssh/known_hosts file