One common response to the RIAA's legal campaign against P2P uploaders is that filesharers will simply move to darknets where the RIAA's spies won't be able to follow. There is something to these arguments. The smaller a darknet, however, the more difficult it will be to find more obscure files. Thus, there will be growing pressure for the users to either opt for a legitimate download service which has convenient access, or to grow the darknet. Unfortunately, the bigger a darknet gets the less manageable it becomes and the easier it is to compromise.

A perfect example of this comes from The Register, which reports that anti-spam activists have infiltrated various spammer forums (Spam fighters infiltrate spam clubs):

Steve Linford of Spamhaus said spammers know this [that their "private" forums have been infiltrated] already but they don't know who amongst their number is working for the other side. In theory the members-only forums of these sites is accessible only by invitation and only to individuals who have a proven track record in spamming.

Darknets for filesharing without fear of lawsuit can work, but only if they remain among small groups of friends known to each other. Once a darknet grows beyond a small group of people known to each other, they become ripe for infiltration. It is between the inconvenience and administrative costs of darknets and the current, excessive price of legitimate downloads that the P2P filesharing answer will be found.

via Slashdot