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<a href="http://freenode.net/policies.shtml#proxies" target="_blank">http://freenode.net/policies.shtml#proxies</a>
Open Proxies, IIS and Appeals

Like many interactive networks, we've had our share of problems with denial-of-service attacks. As a result, we've had to develop a variety of measures to reduce the impact of such attacks. freenode may block access to users whose IRC clients run on hosts with open proxies, IIS servers or other categories of software determined to present special risk to our server environment. We resthe right to use automation to attempt to detect such software on your host, as you connect to our servers, while you remain connected to the network and on occasion during post-connection analysis. Your use of the network signifies your acceptance.