Universities are devising ways to figure out your social insurance number from info on your Facebook and Twitter accounts.
Of course, you think this doesn't apply to you because you don't post your date of birth on your Facebook account. But what if your friends post happy birthday wishes on your wall? If they are even remotely civilised, your friends won't refer to your age but that may not even matter.
And even if you don't list your hometown on your Facebook or Twitter account, there are computer mining programmes which will flag any mention of towns on your wall or your friends' walls until you or someone else identifies it as your hometown in passing.
A date of birth and hometown are enough to find the first three digits of a North American social insurance or, in the U.S., social security number. From there, further information mining can reveal the rest of your number and open the door to identity thief, or just spying, and the unravelling of your entire life.
Your friends are also used for looser forms of information gathering, the kind that governments and companies feast on, your sexual orientation (based on the number of gay friends you have), your political alliances, your purchasing power and habits. And so on.
The accuracy of such information gathering isn't perfect but computers are getting better at figuring you out.
An enlightening New York Times article reveals that the film rental company Netflix was able to increase its prediction of customer rentals by ten percent based on an analysis of customer rental history.
Surely, there is somebody out there analysing the quiz answers Facebook users give. There's a reason for all those movie apps on Facebook, why they invest in hundreds of quizzes and ask for your ratings. It might even be mining those dreaded "list your 1000 favourite movies" Notes friends trade on Facebook. Although current privacy settings offer more assurances, there used to be a time when adding an application on Facebook meant giving the app unbridled access to your account forever, whether you kept the app or not.
Facebook isn't the only source of information: "By examining correlations between various online accounts, the scientists showed that they could identify more than 30 percent of the users of both Twitter, the microblogging service, and Flickr, an online photo-sharing service, even though the accounts had been stripped of identifying information like account names and e-mail addresses."
Jon Kleinberg of Cornell tells the NYT: “When you’re doing stuff online, you should behave as if you’re doing it in public — because increasingly, it is.”