In addition, any unsolicited advertising can also be an offence, depending on where you live. No commercial entity in Australia, for example, is permitted to advertise via the Internet without the prior express consent of the receiving party. Government and charities are exempt but few such correspondence originates from those sources anyway from my own experience. I think this is something that governments around the world have to look at emulating.
Personally I find unsolicited advertising an insult and as an oper on an IRC network I can say that my way of dealing with any advertising = a sudden and instant k:line.