So what happens when there is illegal content on a public computer?

Sometimes the owner of the public computer will put up anti virus programs (mcafee, norton etc) otherwise they would be going through new computers every day with how easy it is for someone to install a bad file. As of the legal status, im not a lawyer, but i think if the owner has put up substantial protection, it is out of their control what the users can do on the computers that is not filtered.