Some might quibble over the distinction between privacy and security. They are closely related. Sometimes inextricably, as in the case of more than 300,000 credit card accounts that were stolen from CDUniverse.com in January, 2000. The thief posted these to his own website, and more than 25,000 of these were given out before the culprit was stopped. (See the full story on internet.com.) What do Victoria's Secret (link no longer available), and the federal government have in common? They too, have had compromised systems.
Identity theft is big business and a big problem. It can be a tremendous headache and take inordinate amounts of time to clear up, if it happens to you. But there are some bright spots; here's an example of a large operation that was shut down by the Feds. Also, California's Office of Privacy Protection is a great resource on preventing identity theft and on what to do if it happens to you.
For practical information on keeping your computer secure, visit the security authority, Gibson Research. Other sites which can help you evaluate your system include the Port Detective, Security Space,