While I can not guarantee that the AAC is completely safe(I still haven't gotten in touch with an anonymous member to penetrate this aac xD), I have failed to find a security hole so far, nobody have reported any issues with it related to the security. So far we have moved from Znote AAC 1.0 to 1.2, and the AAC is still declared as safe in all those versions.
Over a month has passed and no security issues has been detected. I think the biggest reported suspicion on a security hole was in the admin panel, but in order to do anything here, you need admin access. And why the heck would an admin hack himself.
So yeah, I can pretty safely say that as far as I know, this AAC is safe.