see security warning by the author Simon Tatham http://lists.tartarus.org/pipermail/putty-announce/2013/000018.html

"All the pre-built binaries, and the source code, are now available from the PuTTY website at

http://www.chiark.greenend.org.uk/~sgtatham/putty/ http://www.chiark.greenend.org.uk/%7Esgtatham/putty/

This is a SECURITY UPDATE. We recommend that _everybody_ upgrade, as soon as possible.

This release fixes multiple security holes in previous versions of PuTTY, which can allow an SSH-2 server to make PuTTY overrun or underrun buffers and crash...."