Liability Consequences of Co-Blogging
Co-bloggers are exposed to liability for copyright infringement, trade secret misappropriation, and a variety of other claims putatively covered by 47 U.S.C. Section 230. Let’s consider each of these important issues separately.
A blogger who publishes copyright-infringing content via a blog may be directly liable for infringement. The fact that the medium is a blog doesn’t affect the infringement analysis. In addition to the blogger’s direct liability, any co-bloggers who are partners or employers of the infringing blogger are also automatically liable for that infringement.
However, even co-bloggers who are independent contractors or employees may face contributory or vicarious liability for a blogger’s infringement:
- Contributory liability occurs when the defendant, "with knowledge of the infringing activity, induces, causes, or materially contributes to the infringing conduct of another," .
- Vicarious liability occurs when the defendant "has the right and ability to supervise the infringing activity and also has a direct financial interest in such activities." 
The precise contours of contributory and vicarious copyright infringement for online activities are subtle and dynamically changing, so they’re beyond the scope of this brief discussion.  Generally, bloggers face a nontrivial threat of copyright infringement for their co-bloggers’ activities. Bloggers often work closely together and share administrative responsibilities, which may translate—when legally scrutinized—into the requisite level of knowledge of or control over their co-bloggers’ posts.
In theory, 17 U.S.C. Section 512 might mitigate some of this risk. Congress enacted Section 512 to give online service providers some relief from copyright liability committed by third parties. Section 512 could apply when a blogger acts as a service provider for the publication of third-party content, such as comments posted by blog readers or even guest blogger contributions. If Section 512 applies, the safe harbor would limit the blogger’s liability. Thus, Section 512 could be the cornerstone of a blogger’s defense against copyright infringement claims for third-party posts.
However, in practice, Section 512 won’t help in most co-blogger infringement lawsuits, for several reasons:
- It’s unclear when a blogger might qualify as a "service provider" to co-bloggers. Section 512 defines "service provider" broadly,  so the statute could cover bloggers. However, based on their cooperative interaction, co-bloggers may not be legally independent enough for one blogger to be deemed the "service provider" of another co-blogger.  Thus, co-bloggers may act as "service providers" to third parties, but not to each other.
- The case law interpreting the Section 512 safe harbor is mixed. Some cases interpret the safe harbor fairly narrowly. As a result, the safe harbor has proven less useful than defendants initially hoped. 
- Few blogs satisfy the numerous technical prerequisites for Section 512 eligibility, such as registering their websites with the U.S. Copyright Office.  To assess this issue, I searched the Copyright Office’s database of Section 512 registrations on April 18, 2006  and found only 10 registrations containing the word "blog."  Admittedly, this search is neither rigorous nor exhaustive,  but it does reinforce the possibility that a trivial percentage of blogs qualify for the Section 512 safe harbor. 
Without the Section 512 safe harbor, and given sometimes expansive applications of contributory and vicarious copyright infringement, bloggers appear to face significant copyright infringement exposure from co-blogging.
Misappropriated Trade Secrets
A blogger who publishes a third-party trade secret via the blog may be liable for trade secret misappropriation. Partners or employers of the misappropriating blogger could be vicariously liable if the misappropriation occurred in the scope of the partnership or employment. In other circumstances, the co-blogger liability analysis is indeterminate. To my knowledge, no published cases have addressed a website operator’s liability when a third party posts misappropriated trade secrets to the website.  At minimum, I think that co-bloggers won’t face such liability without some scienter about the misappropriation.  It’s also possible that such liability is preempted by 47 U.S.C. Section 230. 
Except with respect to copyright infringement and possibly trade secret misappropriation claims, a co-blogger’s liability for almost all other tortious content published by another co-blogger putatively is covered by 47 U.S.C. Section 230. Under Section 230, a party generally is not liable for tortious content posted by someone else  other than claims based on intellectual property, federal criminal law, or the Electronic Communications Privacy Act (ECPA). 
Section 230 is an exceptionally powerful defense. For example, if a guest blogger publishes a defamatory blog post, Section 230 should absolutely insulate all co-bloggers from defamation liability—regardless of the co-bloggers’ scienter,  editorial role,  or financial benefit from the publication.  Further, Section 230 typically ends the lawsuit on a motion to dismiss, making these lawsuits comparatively cheap and quick to defend.
Clearly, bloggers will want Section 230 immunization for their co-bloggers’ activities. However, there may be situations in which a co-blogger might not be able to claim Section 230. Section 230 applies only when "another information content provider" provides the tortious content. Even if a blogger edits or obtains ownership of a third party’s content, the content still will be provided by another information content provider, so long as the third party had any responsibility for developing the content.  However, if a blogger employs the co-blogger who publishes the tortious content, the blogger-employer may be deemed to be the information content provider.  The same result probably occurs with publications by partners in a blogging partnership; in that case, the partnership may be deemed the information content provider.
Thus, Section 230 may not insulate tortious publications by employees and partners. We would expect that plaintiffs will allege that co-bloggers are partners or employers, to avoid the otherwise terminal effect of Section 230 on their lawsuits. At a minimum, these allegations may allow the lawsuit to survive a motion to dismiss. As a result, depending on the nature of the co-blogging relationship, the potential loss of the Section 230 defense exposes bloggers to significant, unexpected liability.