Internet users are being warned that filters designed to prevent children seeing potentially harmful Web sites often let pornography and terrorist propaganda slip through.
Tessa Russell, senior researcher at the British Consumers' Association's magazine Computing Which? said: 'We tested six of the most popular filters, which often failed to block offensive sites, and in fact barred innocent ones because they can't judge the context of words.'
Investigators tried to visit 15 pornography sites, five about explosives and bomb-making, four explaining how to hack into computers, five racist or fascist, four about illegal drugs, and five that promoted illegal activity.
All six filters let through a Web page explaining how to make a pipe bomb. Four allowed access to an anarchist site with sections on terrorism, assassination techniques, how to break someone's neck, credit-card and ATM fraud, and a recipe for making the drug LSD.
All of the filters allowed the user to enter the British Nazi Party's home page and see racist information from the Ku Klux Klan, and they all allowed access to a bulletin board on the drug ketamine, which explains how to obtain it illegally.
But many denied access to innocent sites, such as that of Middlesex County Cricket Club, because they were programmed to reject certain words.
