Technology giants Google and Facebook are the most visible exemplars of a new generation of business that profit by collecting and exploiting masses of data on individual citizens. This talk will explain what these companies do and explore the implications. It will revisit the infamous Cambridge Analytica case, dissecting what happened and how, as well as the ensuing social and ethical implications. Amongst other issues, it will discuss whether the concept of privacy as we have known it is obsolete, and whether abuses of big data are a major risk to democracy.