Despite all the openness of the Internet, there are still places you cannot saunter into on the Web. You must be invited.

These are “darknets”: exclusive peer-to-peer networks in which membership is based on circles of trust, whose activities are veiled from the general public. And though people who are adept at configuring servers and comfortable with File Transfer Protocol have used such systems for years, a spate of new online services aimed at everyday users is sure to draw new attention to under-the-radar file sharing.

Darknets, like their peer-to-peer predecessors Kazaa, Napster and Gnutella, allow users to browse and download digital files such as movies and music from other people’s computers. But while Napster and its ilk have allowed unrestricted access to files on any of the millions of connected computers, darknets are more discriminating. In a darknet, users get access only through established relationships–and only when they have been invited to join. This selectivity promises greater privacy, regardless of whether the networks are used for sharing personal or pirated media.

File sharers may be enthusiastic about the possibilities such services provide, but there are questions as to whether any new service facilitating file swapping can avoid the legal scrutiny that has hampered open-access file-sharing systems.

Grouper, among the largest of the new services, hosts more than 100,000 private groups. Users can build their own darknets or request admission to thousands of publicly listed clubs whose members can browse through group folders, download files and communicate by instant messaging or group blogs.

A Bible group on Grouper, Deepthings, shares e-books and audio tapes. Needles and Pins offers sewing patterns. Skater Paradise posts skateboarding videos.

Grouper is currently a free service, and contextual ads in its group directory help generate revenue. Soon the company will include video ads and the option to buy photo prints or CDs. The people behind Grouper say they hope to eventually offer a premium service stripped of ads and the ability to control a PC from afar.

Although unauthorized versions of copyrighted material do sometimes drift across the network, the company says it makes great effort to distance itself from illegal activity.

“Our intent is not to circumvent the copyright world,” said Josh Felser, a co-founder of Grouper. “This is about personally generated content.”

Felser and other advocates of commercial darknets think they are fulfilling consumer demand for what might best be called personal distribution, a medium whose potential content expands with every video-equipped cell phone and pocket-size digital camera bought.

“The big play for us is personal video,” Felser said last month, as he toyed with a moviemaking digital camera in his office in Mill Valley, Calif. “Personal video is everywhere, and people are wanting to share video that they create.”

Fighting piracy
To prevent piracy, Grouper limits the file-sharing capacities on its network. Instead of letting members download music, for example, users are allowed to listen only to others’ MP3s in real time through FM-quality streams. Grouper also limits groups to 50 people, and adds a whistleblower feature so members can call out illegal activity.

But their methods are not foolproof. Conspiring group members can change music file extensions or compress album folders to allow downloading, as does the group Only Zipped Music, and there is no means to block pirated software and crack codes, which are circulated in groups like Krakk’d, Warez and Xbox Gamez.

Felser and his partner, Dave Samuel, say they feel that their self-regulating efforts allow them to continue courting the media industry. “We want a company that gives us the ability to partner with other media companies, and eventually, an exit strategy,” said Felser, who sold their previous enterprise, an Internet radio broadcaster called Spinner.com, to America Online for $320 million.

Qnext, another private peer-to-peer network, also tries to distance itself from illegal users in the hope of building a successful business without setting off legal battles. The company packages its service as an all-in-one communications tool with instant messaging, video conferencing and Internet

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