$ which ssh
/opt/local/bin/ssh
$ ssh -V
OpenSSH_5.9p1, OpenSSL 1.0.0e 6 Sep 2011
$ echo $PATH
...:/opt/local/bin:...:/usr/bin:...
$ sudo su -
Password:
# which ssh
/usr/bin/ssh
# ssh -V
OpenSSH_6.2p2, OSSLShim 0.9.8r 8 Dec 2011
# echo $PATH
...:/usr/bin:...