What does it imply to be a whistle-blower?

To find out I went to see the excellent movie Citizenfour. It’s the documentary about Edward Snowden’s divulgation of classified documents. The film doesn’t only give us an over-view of the magnitude of the global system of surveillance that we’re all subjected to but it also led me to wonder about other cases. Such as the one that Sweden is implicated with the Julian Assange affair.