"It raises the accountability for people posting to the category," said Craigslist Chief Executive Officer Jim Buckmaster. "Our well-intentioned users don't want to see illegal activity on the site, either."
Local classifieds and forums for more than 550 cities in over 50 countries, largely free, are a key attraction of the website.
Craigslist already requires that people listing erotic services provide phone numbers, and has begun taking legal action against software companies that help people get around that and other restrictions, Buckmaster said.
Craigslist is not legally required to take such steps - existing law provides immunity to services such as Craigslist for actions taken by their users, said Kurt Opfahl, senior staff attorney for the Electronic Frontier Foundation. However, law enforcement officials can subpoena such companies for user information such as phone and credit card numbers.
In the past, such subpoenas would deliver little information, because the erotic services ads - like most ads on Craigslist - could be posted anonymously.
Under the arrangement with the attorneys general, Craigslist volunteered to begin collecting phone and credit card numbers from erotic services advertisers after Connecticut Attorney General Richard Blumenthal complained about prostitution ads on the site.
Craigslist took a look and decided Blumenthal had a point, Buckmaster said.
"Requiring phone numbers, credit cards and identifying details will provide a roadmap to prostitutes and sex traffickers - so we can track them down and lock them up," Blumenthal said in a statement issued Thursday.
Requiring phone numbers has already reduced the volume of erotic services ads by 80 percent, Buckmaster said. Charging an as-yet-undetermined fee is expected to reduce the volume still further.
The deal brought accolades from groups such as the National Center for Missing and Exploited Children, which joined the agreement, San Francisco Chronicle reported.
"I think it's win-win," said Ernie Allen, president and chief executive officer of the center. "It's an example of Craigslist being concerned and taking a real leadership role in ensuring that these kinds of abuses and illegal activities don't happen."
Sylvia Borelli, founder of Lovings.com, a long-established San Francisco escort Web site, was also complimentary. Borelli said her site has long taken similar measures and more, such as verifying that advertisers are over 18.
"I never liked any of the wide-open personals, because of that possibility of exploitation," she said. The credit card verification system "can also be circumvented. ... But I think that people will start thinking twice, because there is more of a paper trail."
The policy attracted a handful of angry reactions on the Craigslist blog. Commenters accused Craigslist of "caving in to the police establishment" and turning its back on a history of protecting free anonymous expression.
Criticism also came from Maxine Doogan, founder of the Erotic Service Providers Union.
Doogan said Craigslist had provided a place where sex workers could anonymously and safely connect with clients - and vice versa - for free.
"They always end up further pushing into poverty the class of workers who don't have access to those tools of capitalism," she said. "Back to the streets - that's what's going to happen."
On the other end of the criticism spectrum was Trench Reynolds, a pseudonymous crime blogger who tracks Craigslist-linked crime at craigscrimelist.org
"I still say the best way to crack down on that is to do away with the erotic services section altogether," he said. "I think (the deal) will cut down on a lot of the erotic services ads, but I don't think it will cut down enough to put me out of business."
Meanwhile, groups such as the EFF are watching the agreement to see how it works out, said Opfahl.
"Is it going to be a narrowly focused activity that does not spread out to other areas?" he said. "Or will the attorneys general see this as the beginning of a process to get yet more records and ability to obtain the records of online speaking?"
Buckmaster said the company is trying to strike a balance, keeping the erotic services section - in part to keep such ads from appearing elsewhere on Craigslist - but trying to do so responsibly, protecting free speech and preventing exploitation. Hopefully, he said, Craigslist can be a pioneer in this kind of cooperation as it has been on the Internet.
"In our humble opinion this is the way to go, and we would invite other online services to follow suit," he said. "We all would be better off if we all voluntarily do what is necessary to curtail illegal activity on the Internet."