) ▁to ▁another ▁with ▁some ▁sites ▁or ▁specific ▁URLs ▁blocked ▁by ▁some ▁I SP s ▁and ▁not ▁others . ▁Web sites ▁and ▁services ▁are ▁blocked ▁using ▁a ▁combination ▁of ▁data ▁fe eds ▁from ▁private ▁content - control ▁technology ▁companies , ▁government ▁ag encies , ▁N GO s , ▁court ▁orders ▁in ▁conj unction ▁with ▁the ▁service ▁administr ators ▁who ▁may ▁or ▁may ▁not ▁have ▁the ▁power ▁to ▁un block , ▁addition ally ▁block , ▁appeal ▁or ▁rec ategor ise ▁blocked ▁content . ▁ ▁Over view ▁ ▁There ▁are ▁a ▁number ▁of ▁different ▁web ▁blocking ▁program mes ▁in ▁the ▁UK . ▁The ▁high - profile ▁default ▁I SP ▁filters ▁and ▁I WF ▁filters ▁have ▁been ▁referred ▁to ▁as ▁a ▁" p orn wall ", ▁" p orn ▁filter ", ▁" H ad rian ' s ▁Fire wall ", ▁" Gre at ▁Fire wall ▁of ▁Britain " ▁ ▁and ▁the ▁" Gre at ▁Fire wall ▁of ▁Camer on ". ▁However ▁the ▁program mes ▁are ▁usually ▁referred ▁to ▁inter change able ▁or ▁individually ▁rather ▁than ▁collect ively . ▁ ▁Inc iting ▁ra cial ▁hat red ▁was ▁removed ▁from ▁the ▁I WF ' s ▁rem it ▁on ▁the ▁setting ▁up ▁of ▁a ▁police ▁website ▁for ▁the ▁purpose ▁in ▁April ▁ 2 0 1 1 . ▁ ▁The ▁technical ▁measures ▁used ▁to ▁block ▁sites ▁include ▁DNS ▁hij ack ing , ▁DNS ▁blocking , ▁IP ▁address ▁blocking , ▁and ▁Deep ▁packet ▁ins pection , ▁making ▁consistent ▁ver ification ▁problem atic . ▁One ▁known ▁method ▁is ▁I SP ▁sc rap