Get your new version of PuTTY here this release fixes a major security flaw in PuTTY:

2004-08-03 SECURITY HOLE, fixed in PuTTY 0.55 PuTTY 0.55, released today, fixes a serious security hole which may allow a server to execute code of its choice on a PuTTY client connecting to it. In SSH2, the attack can be performed before host key verification, meaning that even if you trust the server you think you are connecting to, a different machine could be impersonating it and could launch the attack before you could tell the difference. We recommend everybody upgrade to 0.55 as soon as possible.