The twitch.tv site and service is being blocked due to the use of non-standard ports of 6667-6669 and 7000 which is used for backdoor access by many IRC like application and therefore a major vulnerability to our users and our network space.
“IRC, by default, does not use encryption. DCC connections (direct connections to other IRC users) might not be encrypted. Some networks expose your external IP address or hostname to others, while others allow you to partially or fully hide it.
There has been numerous cases of client-side bugs which can be exploited to cause a crash or run arbitrary code on your machine.