Clear Putty's Cache

http://tripoverit.blogspot.com/2007/03/clear-puttys-cache.html

For all those of you who have been trying to clear Putty’s cache of host fingerprints (Windows) for development or testing, here is the answer:

1. Open the registry (regedit)
2. Go to HKEY_CURRENT_USER\Software\SimonTatham\PuTTY\SshHostKeys

There you should see Putty’s cache of host keys.
The ‘name’ column tells you which key is for which server.
For example, it will have the format of @: [dss@22:EDA.ipv6.club.tw]

3. Delete the rows that you need.

For Unix users, edit the file "~/.ssh/known_hosts".