For questions about Gitian. "Gitian is a secure source-control oriented software distribution method. This means you can download trusted binaries that are verified by multiple builders"
"Because Bitcoin’s code is open source, anyone able to read code can check for themselves whether it does what it's supposed to do. ... But open source code doesn't necessarily eliminate all risk. Users still need to trust that the software they run on their computers actually reflects the open source code as it should. To eliminate this risk, Bitcoin developers have developed a fierce security policy which goes beyond the open source nature of Bitcoin itself: “Gitian Building.”"