There's no way of telling who (or where) is the "original" source. Most of those evil-doers have dynamic IP adresses (means that their IPs change every now and then)=even if you block one of them, they'll just get another adress in a few hours and pop! they're back in their (annoying) little game.
As stief points out, the best way (right now) is tobe careful at the file sizes and see if this or that file size would be befiting (heh) of a decent-quality file

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ADSL anything from 3 to 8Mbps/around 1024kbps

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