How secure are Github’s private repositories?

Although I do not like this word, this is the place to use it: GitHub services are not “Enterprise” level. There is a gigantic git repositories collection against a huge userspace. If you switch to a paid account, you can mark some of your repositories “private” and limit access to them for a subset of users exists in the system. There is no user level security, no network protection, no extra service continuity options and/or an actual SLA. You need to trust implicitly to your users, and you need to know some good prayers against network and system problems.