Facebook, Google and Twitter: custodians
of our most intimate secrets

The next time you hear the phrase "internet privacy", don't think of teenage infatuations heatedly committed to Facebook, of lads puking down their Ted Bakers and sticking the cameraphone footage on YouTube, or of some hack writer tweeting about the progress of his colonic cancer. No, consider instead AOL Subscriber 4417749.

In summer 2006, AOL did something unprecedented in the history of the internet: it published a database showing what 658,000 members had searched for over three months. A mammoth exercise, this was also one of the most uncynical ever undertaken by a billion-dollar company – AOL shared the information for free, in the hope it would help researchers understand how people were using the web. It was also scrupulous about the confidentiality of customers. All subscriber details were scrubbed out, so that a login such as LimpCourgette223 became drab old User 338765. The only thing left was a list of 20m search terms.

Except that list, coupled with a little patience, was all anyone needed to yank down AOL's privacy screen. A couple of New York Times journalists showed how easily it could be done. Trawling though the hundreds of searches made by Subscriber 4417749 for local estate agents and gardeners, through to "numb fingers", "dog that urinates on everything" and "60 single men", they tracked down Thelma Arnold, a 62-year-old widow and pet-owner from Lilburn, Georgia. "My goodness, it's my whole personal life," she said as the reporter read AOL's search records to her. "I had no idea somebody was looking over my shoulder."