a lolicon said:
ISPs keep track of who had which IP and when.
If the FBI pays a visit to ISP X and wants to know who had IP xxx.xxx.xxx.xxx at 13:37 on the 8th of May, 2011, ISP X can theoretically give the information out. That is, if you're not lucky enough to have an ISP like Bahnhof :P
What is almost impossible to prove is that the person whos name is on the bill is the person who committed the offence. Not because the IP is dynamic, but because the IP doesn't necessarily identify a person.
The thing is both WEP and WPA are easily cracked which gives plausible deniability ISP records themselves are not exactly secure either.
It would be easy enough for said scumbag to have hired a blackhat with no scruples to mess with the logs.
Most even outright thieves draw the line at doing anything to help the copyright whores.
Still I think it would be fun to meet the CEO of this company in an alley somewhere.
I tend to be very paranoid online and use a lot of block lists, proxies etc.