The most important gatherer of personal information in the country is the Federal Bureau of Investigation. It keeps a database of over 90 million fingerprints, which can be accessed by other law enforcement agencies. It also has an extensive database of DNA, the most specific marker of personal identity. The bureau's ability to collect information expanded following the terrorist attacks of Sept. 11, 2001. It now tracks a large portion of mail, cell phone traffic and Internet activity of people it deems suspicious.

Thanks to advances in technology, however, there are also now numerous private enterprises that track and record your every move. Although they don't usually give out this information, there are often worrisome leaks and security breaches where they inadvertently release sensitive information about their customers. Taken together, these industries have data on where you are, who you are communicating with, how you are earning your money, how you are spending that money, as well as the hobbies and interests you are pursuing...