Edward Snowden was a consultant for the US National Security Agency's signal intelligence service NSA. He was upset by what he believed were intrusions into people's privacy: telephone interception, hacking of people's computers and mail intrusion.

In the summer of 2013, he sued for a meeting with two journalists in Hong Kong and handed over millions of secret documents, a meeting that led to a large number of disclosures.

Moving to Sweden, the documents showed that FRA, the Swedish Defense Forces radio station, worked close to US intelligence services.

The publications came to be the start of one of the largest cat-and-rat games in world history.

See the clip above to find out more about what happened next.