Attorneys general in 18 states demanded that Craigslist remove its adult services section last week, the latest clash in a long-running conflict over online sexual ads that is likely to lead to a court battle, congressional debate or both, legal experts say.

"Eventually we're going to see something," said Jason Schultz, assistant professor at the UC Berkeley School of Law. "There has been political pressure building to try to pass new laws or to sue Craigslist criminally."

How any such efforts turn out, however, is more difficult to say.

At the heart of the issue is an open legal question: What responsibilities do websites have to recognize and stop criminal activity facilitated through their properties?

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The Digital Millennium Copyright Act and Communications Decency Act generally protect online publishers from the illegal actions of third parties on their sites, particularly in regard to matters like copyright and defamation. But there are narrow exceptions in the latter law when it comes to criminal statues.

The attorneys general would probably use this window to pursue a criminal case, charging Craigslist with aiding and abetting illegal activity. Any legislative push, meanwhile, would be likely to seek to more specifically define those exceptions.

The San Francisco company is the focal point of the debate, as the leading online classified ad site - and what one critic has branded the "Wal-Mart of online sex trafficking." But any ruling or new laws could have broad implications for how many Internet sites operate.

"If you impose liability on Craigslist, YouTube and Facebook for anything their users do, then they're not going to take chances," said Brian Carver, an attorney and assistant professor at the school of information at UC Berkeley. "It would likely result in the takedown of what might otherwise be perfectly legitimate free expression."

Concern for that possibility is what motivated the broad immunity in the Communications Decency Act in the first place, under the belief that law enforcement should pursue criminals and not the platforms they're using to pursue crimes, he said.

But complaints from certain politicians and groups like the Rebecca Project for Human Rights concerning ads that may promote prostitution or child trafficking clearly show the argument hasn't satisfied all parties.

South Carolina Attorney General Henry McMaster threatened to file a criminal suit against Craigslist and its executives last year, as he was ramping up his campaign for governor. A U.S. District Court judge rejected the company's request for a permanent injunction against such a case this month, clearing the way for it to move forward.

But McMaster lost his bid for the Republican nomination in June and isn't running for re-election as attorney general. It's unclear whether he will continue to pursue the case. An inquiry to his office wasn't returned before press time.

Rep. Jackie Speier, D-Hillsborough, said she has set up a House Judiciary Committee hearing next month to explore how websites such as Craigslist are being used to "facilitate criminal activity." A specific date hasn't been scheduled, she said.

Speier recently met with a minor whose pimp advertised her on the site and forced her to have sex as many as 10 times a night, she said.

"It's a crime against these young women," she said.

Tough legal questions

But any lawsuit or legislation concerning the responsibilities of Internet sites in these cases must grapple with some difficult legal questions:

-- Can a company like Craigslist be expected to distinguish between ads for legal services like massages and escorts, and those that wink at something illicit?

-- Is the company more culpable for such ads than the alternative weekly newspapers whose pages are filled with them?

-- Would Craigslist have to catch every instance of illegal offerings in its classified ads to be in compliance - or just 80 percent, or a mere 50 percent?

"No one has set a standard in a court of law for what that looks like," said Schultz, adding that a lawsuit isn't a slam dunk for either side.

It also isn't clear how much removing the adult section would accomplish, as the ads may simply migrate to other parts of the site - or, for that matter, spill onto rogue, offshore Internet services. That could make it more difficult to monitor these crimes and prosecute pimps, as Craigslist retains information about the posters of ads and cooperates with law enforcement, Carver said.

Tackling the problem

Demanding censorship on a website based in San Francisco may be an easy way to score political points, but it's an ineffective way of tackling the underlying problem, said Jim Buckmaster, chief executive of Craigslist.

"Is moving advertising around our best hope for addressing these harms?" he said. "Then the ads fall under personals, and how long before the demand is that we shut down personals? And where do those ads go next? What other sections of our site would they like us to shut down?"

The practical legal questions have been further clouded by heartrending headlines in recent months. A series of stories around the nation have described how Craigslist has been used by pimps to operate prostitution rings and promote child trafficking, or by johns who went on to commit violent crimes against women.

"The increasingly sharp public criticism of Craigslist's Adult Services section reflects a growing recognition that ads for prostitution - including ads trafficking children - are rampant on it," a group of 17 state attorneys general said in an Aug. 24 letter to Buckmaster and Craigslist founder Craig Newmark. Massachusetts' attorney general echoed that concern in a separate letter sent to the company.

"We recognize that Craigslist may lose the considerable revenue generated by the Adult Services ads," the joint letter continued. "No amount of money, however, can justify the scourge of illegal prostitution, and the suffering of the women and children who will continue to be victimized."

The statement clearly accuses Craigslist of profiteering, but fails to mention that the company didn't charge for the ads until pressured to do so by those same attorneys general. In late 2008, with the top cops from more than 40 states demanding changes, Craigslist began requiring posters to provide a working phone number, a small per-ad fee and credit card verification to encourage compliance with the site's guidelines.

The company donated the net revenue from those ads to nonprofits up until at least this spring, at which point incidents like nonprofits ripping up their checks in front of media cameras led Craigslist to stop discussing nonprofit contributions publicly, Buckmaster said. Over the years, Craigslist has famously turned down opportunities to wring maximum profits out of the site.

Screening images

"To be painted as callous, uncaring, all-about-the-bottom-line capitalists is absurd," Buckmaster said.

He insists that Craigslist does far more than other websites, as well as many print publications, to exclude these sorts of ads. Since the spring of 2009, the company has manually screened the images and text of every ad submitted to its adult section before it is published. Any that indicate the involvement of an underage person are reported to the National Center for Missing and Exploited Children, he said.

"We're not content with that status quo, and we're working with nonprofit partners to take that section of the site to the next level in terms of the things we do," he said. "We're pouring enormous amounts of our time and energy into doing the best job that we can to respect our users' wishers, and to do the best we can under the tutelage of nonprofits to address the issues that are inherent to this category of advertising."