http://mina.naguib.ca/blog/2012/10/22/the-little-ssh-that-sometimes-couldnt.html
Stuff like this makes me miss being a network admin.
Archives
The below is a great story and a good lesson on the importance of cryptographic key size.
http://www.wired.com/threatlevel/2012/10/dkim-vulnerability-widespread/all/
Related to this, if you run a mail server consider looking into DKIM. It is an interesting addition to the Internet mail architecture and not that hard to enable via a sendmail milter (OpenDKIM).