They should let you know so that you can report the site or the email server about the violation. It's not illegal to have nudity on the web, but it is illegal to solicit children about this. You can also use programs to block such sites, but these are not completely failsafe. Unfortunately Cyberstalkers are very real. It's important to remember that we don't really know who we're talking to on the other end of the computer.
People can say they are anyone they want to be.
Sometimes cyberstalkers disguise themselves as teenagers and try to befriend people. They try to obtain information like email address, phone numbers or street addresses. Cyberstalkers can be men or women, even teenagers. Online you can report a stalker to Cyber Angels or SafetyED International and they will help you.