'This oversteps a boundary': teenagers perturbed by Facebook surveillance

News that Facebook shared teens' details with advertisers throws focus on firm's ability to mine the data of its 2 billion users - and raises serious ethical questions

• Facebook told advertisers it can identify teens feeling 'worthless'

We know that Facebook keeps track of every like, click and post we make to its platform. If we often check in at airports, it's not surprising when we are shown airline ads. If we like a load of electronic music artists, we don't balk when we see a promo for a festival where some of them are playing. We have grown accustomed to it, and there's some visibility about what's going on in the black box.

Related: 'I'm an ex-Facebook exec: don't believe what they tell you about ads'