Wow, thanks alot for these detailed answers.
But today another question came to my mind.
Lets say we know, that our neighbar uses Bitcoin, and we also know that he will receive a payment soon (maybe because he owns an internet shop and accepts bitcoin as payment option).
Also, we know that he uses WLAN and his network is unsecured or weak protected. Same goes for router configuration.
We now could log into his router configuration, change the ip adresses for the forwarded port 8333 to our system ip. Now every payment would be received by our bitcoin client.
Is this actually going to work ?
I know this is highly criminal and the scenario is .. well, lets call it “uncommon”, but in theory it should work, right ? (Not that I have an interest in harming people, but I know that criminal people will try many ways to get some money.)
BTW: same should work when you are on a LAN party with unprotected router config.
Edit: Or are these scenarios totally impossible because no matter which ip adress uses the port, the payment will go to the bitcoin or ip adress that was defined from the payer ?