Answer: The Talmud teaches that if a fisherman set up baited nets in a public area and as a result a great number of fish started clustering in the area, other fishermen are instructed to distance themselves up to four kilometres away from his nets. Because it was a direct result of his efforts that the fish came to the area, other fishermen may not poach and reap the profits of their fellow fisherman's labours.
Besides for the obvious implications that this Talmudic concept has for many laws pertaining to economic competition, our rabbis make another far-reaching principle based on the "fisherman model": Just as the fisherman who baited the nets is legally entitled to the fish that have gathered as a result of his efforts, so too anyone who has invested efforts in attaining a certain goal, possesses exclusive rights to the resulting profits of that investment. It makes no difference whether this creation is tangible or not, if the creator has utilized energies in the creation of his work, he is entitled to enjoy the fruits of his labours just like the fisherman who diligently baited his nets. A violation of this right is deemed as "Hasagat Gevul" - "Illegal encroachment" on someone else's business rights.
Another principle discussed in the Talmud that can serve as the Halachik basis for copyright laws is the concept of "Shiyur" - "Retention": The Talmud speaks of one who sells his sheep yet retains for himself the rights to the sheep's sheerings and offspring. The buyer may do whatever he wants with the animal but his ownership is limited because with regards to the sheerings and offspring, the animal is considered as if it still belongs to the seller. Based on this principle one who sells a product can stipulate that he is only selling the rights to derive personal enjoyment from it but is not selling the rights to copy or further produce it. These rights are retained by the creator/seller. The limitation of this principle is that this line of reasoning is only valid if it is specifically stated that the sale is of a limited nature with all rights of reproducing retained by the seller.