This is not uncommon for this age. Curiosity about female bodies and sexual acts are a normal part of sexual "growing up" I would approach this in a number of ways. First, acknowledge that you are checking his computer history. he needs to know that is a parents job. Remind him of the danger of watching a video or websites that may have people under 18 y/o on it. It's kiddie porn which is illegal to download, possess or copy. Second, there may be a police person luring him into contact. third, remind him that it is an abuse of women and men and that what he sees may be stimulating, but does not necessarily portray loving adult sexual behavior. Discuss whether his friends led him to these sites or did he find them on his own. It is a good time also to bring up issues of sexual identity. Boys at this age can often be searching the web for friends. Be reassuring, but remind him of how unsafe that can be.
How you handle this is very important. Don't confront. Don't have a sit down with dad. handle it individually. Best wishes and good for you for dealing right on.
Wayne Yankus, MD, FAAP
expert panelist: pediatrics
Trying putting a child safety program on your computer to block those site from him. I did it after I found the same thing. He was 11 at the time too. I found out a neighbor kid showed him after the kid moved away. And talk to him about the dangers of it.