It's actually very easy, because only one person is compiling 'official' bitcoin client which is used by thousands users, force this person to corrupt, backdoor 'official' client and you can destroy bitcoin in just few second... and don't give me argument you 'can Compile it yourself' 90% use standard bitcoin-qt client.
um. no.
it's not like in the movies where a person pushes the big red 'hack' button.
open source has a series of checks and balances with github builds.