Security, Elgg

I'm looking for a platform to develop a social network. The most important thing for me in order to choose a particular platform, is that the safety is emphasized for the users.

Is there anyone here who can say something about how the security is regarding Elgg?

In a social network based on Elgg, have the users the opportunity themselves to precisely manage who can see their activities etc?

What kind of security mechanisms have Elgg to protect the users of the network?