I don't have a smartphone specifically because I believe they are insecure by design, at least one company and a whole raft of employees there have access to it and that's before we get into automatic updates of the software on those devices and so on.
When I say I'm pretty sure that this machine wasn't compromised that is because I'm utterly paranoid when it comes to stuff like this. Possibly not paranoid enough - given the evidence just obtained...
That's a good one: on a server with an asymmetric encryption system (different decryption key than encryption key) the decryption key is not stored in any automated system, the back up is 'pull' from that one server inbound to this machine.
I guess it is theoretically possible that someone broke into the backup server but it too is locked down pretty good, to the point that if I want access I'll have to get into the car and go there in person. Call me paranoid :)