For those who like to use vnc to work with remote computer, you should be aware that the traffic is not encrypted. Please refer to tightvnc faq page for information about this. Just like what recommended in the faq, ssh is required to secure the traffic.
Create a tunnel between your local and remote computer, and one way to do this is:
$ ssh -CNT username@remote_computer -L 5901:127.0.0.1:5900
Now, simply set your vnc viewer to access localhost with port 5901.
An example of using vncviewer is:
$ vncviewer localhost:5901