In case you use PuTTY, the free Windows SSH client (and I know a lot of people who do), there is a rather nasty security vulnerability in it. Simon Tatham has just announced to the mailing list "…it could be as bad as allowing the server to execute code of its choice on the client."
Anyway, the best thing is to mosey on down to the PuTTY website and grab a copy of the latest version, 0.55. More details about the security hole will be found at the site.