We find out how Big Tech companies may know more about you - than you do.

Host Claire Graham talks to the BBC's cyber correspondent for the BBC World Service Joe Tidy, about how Big Tech companies not only track what you do online – but what your friends do – and what your friends of friends do – to then target you through marketing.

Billions of people access Big Tech companies on a daily basis – to interact on social media sites – but at what cost – your privacy?

Produced by Cathy Young for the BBC World Service.