This is two paragraphs of a long article. He mentions flash cookies which you can get rid of.
Last month, the British advertising giant WPP boasted that it had just created the world’s largest database of individuals’ online behaviour: profiles of 500 million people, covering, it says, almost 100 per cent of the people online in the countries in which it operates, including the UK, the US, Australia and eight others. The firm said it was pooling data from many of the world’s major websites and networks of online advertisers and adding it to information purchased from traditional market-research firms that assemble real-world data such as what people are buying in high street stores. That real-world information has been “anonymised”, WPP says, before it is added to its database of cookies.
Ashkan Soltani, the privacy researcher who co-authored the Berkeley study, told a Congressional hearing earlier this year that online tracking has become so sophisticated that advertising networks can serve up ads for depression medicine to people who have searched for “depression” on a health site, and that recent computer-science research suggests it is often quite easy to identify the people whose profiles include so much supposedly anonymised user information. Worse, ad networks always seem to be one step ahead of even the most privacy-minded internet users. Many now use “Flash cookies”, served from sites that use Adobe’s programming language Flash, which have the ability to restore other deleted cookies.”