What is mass surveillance?

Mass surveillance is the pervasive surveillance of an entire population, or a substantial fraction thereof. Mass surveillance may be done either with or without the consent of those under surveillance, and may or may not serve their interests.

For example, Carnivore is a system implemented by the Federal Bureau of Investigation that is analogous to wiretapping, except in this case, e-mail and other communications are being tapped instead of telephone conversations. Carnivore is a customizable packet sniffer that can monitor all of a target user's Internet traffic. It is a form of policeware. U.S. government officials have neither confirmed nor denied much about the physical or logical workings of Carnivore, but there are some facts that are generally agreed upon.

Sources:
http://en.wikipedia.org/wiki/Mass_surveillance
http://en.wikipedia.org/wiki/Carnivore_(software)
http://www.wired.com/politics/law/news/2001/08/45798
http://www.privacyinternational.org/article.shtml?cmd%5B347%5D=x-347-559597