theunholy@ubuntu:~$ sudo ssh localhost
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@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
3d:c6:13:19:8b:2e:de:9e:3b:cf:47:6b:f6:c6:f1:dc.
Please contact your system administrator.
Add correct host key in /root/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /root/.ssh/known_hosts:1
  remove with: ssh-keygen -f "/root/.ssh/known_hosts" -R localhost
ECDSA host key for localhost has changed and you have requested strict checking.
Host key verification failed.