NSA whistleblower Edward Snowden is known to be a long-time advocate of free and open source software. Speaking at an event via video conferencing, he said that transparency of free software convinced him to use TOR, Tails, and Debian, that helped him to expose the secrets of American government.
http://fossbytes.com/snowden-free-open-source-software-like-debian-tor-didnt-trust-microsoft/