I don’t have special insight to offer here, but I want this placeholder page here to distribute wake-up calls to my friends who aren’t terrified about surveillance in Australia. Should be broadly applicable.
For some basic, good-enough-for-now remedial security tips, please see confidentiality for the masses and confidentiality for journalists, or for general philosophy, information security.
For example, they can see through your walls with wifi. They can identify you by your heartbeat at a distance of 200m. They can learn your passwords by listening to you type. even your printer is tracking you
As for who they are, that rather depends. But potentially very many different agents. That is exactly the problem.