I don't know much about the technical details, but this thought occured to me the other day and i don't know any other 'techie' people to ask.
Imagine two computers on the internet, computer A and computer B. My crude understanding is that if A wants to download something from B, A first sends some kind of 'request' to B. B then sends the data and addresses it to A. The ISP then forwards this data to A and logs it as "download usage".
So my question is this: what happens if B sends data addressed to A without A requesting it first?
Does the ISP still forward this data to A, only for A to discard it because it wasn't expecting it? If so, does the ISP have some way of checking that A really did request the data, or does this data get recorded as download usage by the ISP regardless?