I'm using the Livewire in an apartment block and I've used the Livewire utility to setup a private network. Are the network packets restricted to my apartment or can people in other apartments view my Livewire network? How secure is the Livewire network compared to a wireless network using wpa2 and a strong password?
It depends on how your apartment building is wired.
If multiple tenants use the same transformer secondary side, then it's very possible for people to see each other's networks via powerline adapters.
That's why they have an option to encrypt traffic between units that are configured to do so.
Compared to WPA2? Probably not as strong... But given that someone trying to "Crack" a homeplug network has to be in very close physical proximity, it's probably "functionally" equivalent...