It uses a central server to link computers together to avoid the complexity of other peer-to-peer programs such as Gnutella, a file-sharing program popular among the high-tech community.

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But Real DVD doesn't appear to do anything clearly illegal, says Laurence Pulgram, an attorney with Fenwick and West LLP who defended the file-sharing program Napster in its 2001 copyright case.

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Skype, which now has more than 663 million registered users world-wide, traces its roots to a file-sharing program, Kazaa, that grew popular for exchanging pirated music soon after its launch in 2001.

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Pennsylvania State University is using the program to allow its students to access music download service Napster to give them a legal alternative to file sharing.

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