PuTTY's days are numbered
I seem to recall PuTTY has had a mixed history when it comes to security (e.g IIRC there was a period where they had a trojanised copy hosted on the official website for quite some time before it got noticed).
Fortunately PuTTY's days are numbered. One of the best reasons to upgrade to the latest version of Windows (server or desktop) is that it now comes with OpenSSH built-in (you just have to activate the option in control panel).
Linux, OS X and Solaris users of course have no reason to be using PuTTY in the first place. ;-)
P.S. Yes I know some smart alec will come saying that some people "have to use" old versions of Windows. To that I will say, if you really, really have to, then you really, really should know how to take care of yourself in terms of security and probably source your SSH more carefully than downloading a pre-compiled binary off a random website.