Company CEO Jim Buckmaster said this week in a blog post that the site has seen a 90-95% decline in "erotic services" ads in five large cities since it began demanding more information from advertisers last year.

"Beyond the enormous reduction in ad volume, the ads that remain on the site are much improved in their compliance with our terms of use and local laws, in part due to screening measures developed in collaboration with the Attorneys General and law enforcement," Buckmaster wrote. The cities mentioned in the post are Atlanta, Chicago, Los Angeles, New York City and Seattle.

Last March, the site said it would require that "erotic services" advertisers provide a valid phone number, which led to an 80% drop in such ads. In November, Craigslist added a requirement that such advertisers have a valid credit card and began charging for the erotic services ads, with the revenue going to charity. Those changes, which resulted from deals with 40 state attorneys general, led to a further drop in ad volume.

Last week, the Cook County sheriff sued Craigslist for creating a public nuisance by facilitating prostitution. The lawsuit, which seeks an injunction and monetary damages, alleges that the county recently made 156 arrests, at a cost of around $105,000 after monitoring the site.

Internet law experts said that the suit was unlikely to get very far because the federal Communications Decency Act says that sites like Craigslist are immune from state tort lawsuits based on material posted by users.

Craigslist Friday issued a statement in which it said it was "mystified" by the lawsuit. "We assist police forces all over the country, including members of Sheriff Dart's department," Buckmaster stated. "The vast majority seem to understand that craigslist is part of the solution when it comes to combating terrible crimes like human trafficking and child exploitation."

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