A.2.3 Does PuTTY support SSH-1?
Yes. SSH-1 support has always been available in PuTTY.
However, the SSH-1 protocol has many weaknesses and is no longer considered secure; you should use SSH-2 instead if at all possible.
As of 0.68, PuTTY will no longer fall back to SSH-1 if the server doesn't appear to support SSH-2; you must explicitly ask for SSH-1.