Personal data is a hot commodity. All sorts of businesses trade in data concerning what we buy, how much credit we have, where we live, what our interests are. This information is sold to advertisers, who then eagerly use it to more precisely target people that they hope will be interested in their products ? leading to all those annoying catalogs that litter your doorstep, for example, or the junk emails that choke your inbox every day.

Luckily for the advertising industry, modern web users have begun voluntarily providing all their personal details on social networking sites like Facebook and MySpace. Users of these sites happily upload all sorts of personal information about what books and music they like, where they shop, who their friends are, and where they live. While users of these sites may imagine that they control the information on their profile pages, advertisers are salivating at the thought of all that personal data just waiting to be processed, analyzed, and turned into profit.

Recently, both Facebook and MySpace have announced plans to do just that. The president of Fox Interactive Media, which owns MySpace, tells potential clients that "We have an opportunity to provide advertisers with a completely new paradigm." The personal data of MySpace users will be used to generate "targeted advertising" that is tailored to each individual account, using algorithms that assign members to one of 10 main consumer categories.

Not one to be left behind, Facebook has a similar program. They now slip targeted ads into the "news feed," along with updates about the user?s friends on Facebook, where they are sure not to miss them.

Google, which has access to some of the most coveted personal data on the Internet -- your search logs -- has recently acquired DoubleClick, a company that uses browser cookies to track what sites Internet users visit and what commercial advertisements they click while browsing. Google?s senior policy counsel finds it all quite innocent: "Simply put, advertising is information," he said.

While none of this may be illegal, it does have ominous implications, as Cory Doctorow humorously points out in his recent short story, Scroogled. The personal data we now use to keep in touch with friends will soon help corporations target us more effectively. What's to stop this wealth of data from creeping into law enforcement activities?

While it may seem odd to object to potential privacy violations of people who voluntarily share their own info, the bottom line is that users need to know what is being done with their information, and should have the opportunity to opt out of marketing schemes if they choose. Last year, when changes to Facebook's interface made it easier for users to track each other's changes, protests were loud and angry, leading to some changes in policy. Let's hope a similar uproar greets social networking sites' latest decisions to treat their users like products on the open market.

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