The California Supreme Court just held, in Barrett v. Rosenthal, that Internet users who post (to Web sites or discussion groups) material created by others are immune from liability.
Federal law, 47 U.S.C. § 230, provides that "No provider or user of an interactive computer service shall be treated as the publisher or speaker of any information provided by another information content provider." The California Supreme Court held that this protects not just service providers whose sites are used to post material without the provider's intervention, but also users who personally select which material (written by others) to post. (The Ninth Circuit held the same three years ago, in Batzel v. Smith, 333 F.3d 1018 (9th Cir. 2003).) The court also noted:
At some point, active involvement in the creation of a defamatory Internet posting would expose a defendant to liability as an original source. Because Rosenthal made no changes in the article she republished on the newsgroups, we need not consider when that line is crossed. We note, however, that many courts have reasoned that participation going no further than the traditional editorial functions of a publisher cannot deprive a defendant of section 230 immunity.
A long line of cases had already held that when a user posts material on a site, the operator of the site (or of the computer), can't be held liable, even when it's notified of the potentially tortious nature of the activity. Thus, for instance, we wouldn't be liable for libels posted in our comments. But this case, as well as Batzel and some others, apply this principle even to immunize those who actively repost material, rather than just serve as passive conduits for what others post. This means that if a commenter posts excerpts from others' work, even the commentator himself would be categorically immune from liability for the contents of those excerpts, at least unless he's "active[ly] involve[d] in the creation of [the] posting," or unless he's conspiring with the original author.
Note that when I say "immune from liability" or "can't be held liable," this is shorthand for "immune from liability except under intellectual property law, communications privacy law, or federal criminal law," see 47 U.S.C. § 230(e)(1).