Hmmm. This is an interesting question from an older sister (I wonder what the relative ages are). It more usually comes from parents or other adult relatives. Enforced censorship and issues of moral guidance for children are well-worn topics, covered extensively elsewhere. Once you have pugged into the net, porn is immediately available both through explicitly titled sites and downloads and through indirectly named material. Enterprising children can always get round blocking mechanisms — indeed, the resort to filters is often viewed as a challenge to be beaten. The nature of the argument is similar in debates to decriminalise soft drugs and prostitution. If you remove the aura of "illegality", you also remove that part of the attraction to indulge represented by rebellion against authority (legitimate or otherwise). So although a lockable "adult filter" could easily be added (even though it would be lockable in name only to a determined child), it is better to recognise that all children of both genders will, at some time in their lives, be curious about what society deems pornographic. Instead of trying to stamp out that entirely natural instinct to know what is hidden, open and frank discussion is the better alternative. Education is the best filter of all. In default, throw your computer away, ban him from ever logging on to a computer at school, at a friend's house, at a cyber cafe — no, on balance, just give up.