This article describes a problem that may occur when you try to connect to a server using SSH, and how to resolve it.

When you try to connect to a server using SSH, you receive a warning message.

• If your computer is running macOS or Linux, the message is:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
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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.

• If you are using PuTTY on Microsoft Windows, the message is:

WARNING - POTENTIAL SECURITY BREACH!

The server's host key does not match the one PuTTY has cached in the registry. 
This means that either the server administrator has changed the host key, 
or you have actually connected to another computer pretending to be the server.

The most likely cause of this problem is that the RSA fingerprint has changed on the remote server, but the client computer still has the previous RSA fingerprint stored. This often occurs after you install a new operating system template on a server.