[ Thanks to Adam for
this link. ]
“UDP tunneling is an attack that is often overlooked
when manufacturers design wireless hotspot and other firewall/proxy
based devices.“When you try and resolve a domain name, you make a request to a
name server on UDP port 53. The way that a lot of wireless hotspot,
firewalls and proxies work, is that your DNS request is allowed
out, you get the IP for the machine you’re looking for, and
then your request to the IP is redirected to the wireless hotspot
login page, or through a web proxy server.“The problem is, that all port 53 UDP traffic is allowed out to
anywhere, without any kind of authentication. You can therefore
install OpenVPN on a remote server which by default listens in on
UDP port 1194. You can change this with one configuration option to
53, and then edit your client config to connect to the server on
port 53 instead.”