Publishers are worried that the sites could become public troves of illegally uploaded content. In late 2013, Elsevier sent 3,000 notices to Academia.edu and other sites under the US Digital Millennium Copyright Act (DMCA), demanding that they take down papers for which the publisher owned copyright. Academia.edu passed each notice on to its users — a decision that triggered a public outcry. One researcher who received a take-down request did not want to be named, but told Nature: “I hardly know any scientists who don’t violate copyright laws. We just fly below the radar and hope that the publishers don’t notice.”

These concerns are not unique to large social networks, says Price; the same issue surrounds content posted in universities’ online repositories (to which Elsevier also sent some DMCA notices last year). “This is really part of the wider battle where academics want to share their papers freely online, whereas publishers want to keep content behind a paywall to monetize it,” he says, noting the nuance that many publishers allow researchers to upload the final accepted version of a manuscript, but not the final PDF. He has seen fewer take-down notices this year.