The British pornofilter that users should protect against pornography and other unwanted content, also prevents a part of the British access to the German hackersorganisatie Chaos Computer Club. Also another site with information for hackers is blocked.
Also, Hackaday, a website where users information about hacks and tools may be ordered, is blocked. That website is only blocked for a part of subscribers from British Telecom; other telecom providers, the users still have access. The pornofilter, where providers voluntarily to cooperate, it turned out previously all sites with sexual information and to block.
Update, 12:39: such As user hall rightly observes, a lot of people have – in contrast to what the CCC claims – the pornofilter just turned off. That Hackaday only by British Telecom is blocked, is no surprise: that company offers a filter that also sites with information about hacking blocks.