A federal judge has dismissed a public nuisance lawsuit filed by the sheriff of Cook County, Ill., against Craigslist, finding that the Web site is entitled to immunity under Section 230 of the Communications Decency Act.

Sheriff Thomas Dart had argued in a federal lawsuit filed last March that Craigslist facilitated prostitution and constituted a public nuisance by allowing users to post ads for prostitution. He noted that his officers routinely investigated ads posted on Craigslist and that many of those probes led to arrests and charges of prostitution or solicitation.

Craigslist had offered in its Chicago listings an “erotic” subcategory that allowed users to post messages or ads of various sorts. Dart contended that many of the posts contained code words for sex and fees for sexual services. After the lawsuit was filed, Craigslist removed the “erotic” subcategory and replaced it with an “adult” category. The site also offers users the ability to search different ads with a word-search engine.

Craigslist responded to the lawsuit by filing a motion to dismiss based on Section 230(c)(1), which provides: “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.” Craigslist argued that it was an “interactive computer service” that should not be punished for the material posted by its users who qualify as “another information content provider.”

U.S. District Judge John F. Grady agreed with Craigslist in his Oct. 20 opinion in Dart v. Craigslist. He relied in part on the 7th U.S. Circuit Court of Appeals decision in Chicago Lawyers’ Committee for Civil Rights Under the Law v. Craigslist, Inc., which rejected a lawsuit against Craigslist for allowing discriminatory ads in its housing category. In that ruling, the 7th Circuit wrote that “an online information system must not ‘be treated as the publisher or speaker of any information provided by’ someone else.” Grady quoted that statement in determining that Craigslist could not be considered the publisher of the prostitution ads.

Dart contended that Craigslist had knowingly “arranged” meetings for purposes of prostitution and took a more active role than that of an intermediary or traditional publisher by having an “adult” category.

Grady, however, found that Craigslist was an intermediary and did not create any illegal ads. He also reasoned that many of the ads were not illegal. “A woman advertising erotic dancing for male clients is offering an ‘adult service,’ yet this is not prostitution,” he wrote. “It may even be entitled to some limited protection under the First Amendment. Plaintiff’s argument that Craigslist causes or induces illegal content is further undercut by the fact that Craigslist repeatedly warns users not to post such content.”

Dart also argued that Craigslist was not entitled to Section 230 immunity because of its word-search function which enables users to search for prostitution ads. However, Grady quoted the 9th Circuit’s decision in Fair Housing Council v. Roommates.com for the principle that “ordinary search engines do not use unlawful criteria to limit the scope of searches conducted on them, nor are they designed to achieve illegal ends.”

Grady added that Craigslist “does not cause or induce anyone to create, post, or search for illegal content.” He concluded: “Sheriff Dart may continue to use Craigslist’s website to identify and pursue individuals who post unlawful content. But he cannot sue Craigslist for their conduct.”

“The decision represents a reasoned application of Section 230,” said Matt Zimmerman, senior staff attorney with the Electronic Frontier Foundation.

“Dart was seeking to impose civil liability upon Craigslist for content created by third parties and that did not fit into any of the exceptions to Section 230, such as the exceptions for violating intellectual property and criminal laws," Zimmerman said. "Here Dart sought to impose civil liability under the public nuisance theory and Section 230 forbids that. Congress made the decision in passing Section 230 that you don’t make the soapbox liable for the speech that takes place on it.”

Dart told the Associated Press that he was still considering whether to appeal the ruling. “It isn’t that I just woke up one morning and said, ‘Let’s sue Craigslist.' This came after two years and hundreds of arrests off of the Web site, and many of the arrests involve juveniles and human trafficking.”