People, please note that the investigation by the police will be focusing on the Telecommunications Interception Act which governs the interception (inadvertant or otherwise) of anything that is traversing over the Australian Telecommunications Network.
The ATN is any medium and communications device that is directly connected to any Australian infrastructure. This includes all your home routers, all telephones and any other communications medium.
Compare this with the Privacy Act, (which may also apply) it is radically different. The privacy act doesn't really apply here.
Have you ever wondered why all call centres tell you they may record your call for training purposes? That's to get around the TIA act. Otherwise they would be breaching a very significant law.
It is also illegal in Australia to run a spam/malware filter without notifing and having the user agree to a machine intercepting your email. If you don't agree to this, your company or sysadmin is breaking the TIA act and is liable to be sent to jail. (@AussieSysadmins Pro tip: Make sure you have your arse covered.)
Please note that this isn't a money grabbing exercise by the government, it will only cost them money to investigate, prosecute and detain anyone. They will not be sueing Google for money. That's not how the law in Australia works.
Also note that it is not the same as overhearing someone in the street. The privacy act governs that and only applies if the person being overheard has a reasonable expectation of privacy while they were being overheard.
You can connect to any open wifi access point you want, it's when you capture or sniff any of the packets that you start breaching the TIA act and are liable for jail time.
I hope this clears things up for some people.
If you are interested, please have a flick through the TIA act here: