That depends on what you use the Internet for. If you use it to access pornography or to cultivate an adulterous relationship, it is immoral. If you use it to enlighten your mind with wholesome facts and truths, then it is beneficial. Like television, cable, VCRs, DVDs, cell phones, and all technology, the Internet can be easily abused and used for sinful purposes, or it can be used to evangelize and catechize as is done, for example, on the Eternal Word Television Network (EWTN) web page: www.ewtn.com. Books can be used for good or for evil, so one is not limited to the world wide web as a potential source of immorality.
Parents are strongly urged, however, not to trust anyone else in cyberspace no matter how good and trustworthy their teenagers are,. Your son or daughter may not have obscene desires, but pedophiles and child abusers do, and they often impersonate being a teenager themselves to prey on children and adolescents. That is why the Internet is good for young people only if they are supervised. One Internet connection in the house should be attached to one computer which is in full, conspicuous view of everyone in the house at all times.