There is evidence that teenagers have attached pornography to computer viruses. The viruses then spread the material automatically, without the original perpetrator being directly involved. There is a lot of news coverage of Internet pornography. A lot of this is driven by voyeurism, so possiblyly over-estimating the significance of the issues. People do need to learn, sometime, to be wise.
Many people argue that parental responsibility is the core issue.
You had children, now be responsible for them. This view seriously under-estimates the difficulty of being responsible when children often have much better technical knowledge and access to material on the Internet. Teenagers are often unsupervised, and they are ones likely to search out sexually interesting material. A report in the British Medical Journal shows that boys given sex education at school were less likely to take part in under-age sex, and girls were no more likely than otherwise. More research like this is needed.