Police in the US are setting up bogus advertisements on the popular Craigslist web forum to catch prostitutes and their customers.

Officers are answering adverts from prostitutes, and have been posting their own messages to lure people seeking to pay for sex. Police in Nassau County, New York claim to have made over 70 arrests so far.

"Craigslist has become the hi-tech '42nd Street' where much of the solicitation takes place now," Richard McGuire, assistant chief of detectives at Nassau County Police Department, told the New York Times.

"Technology has worked its way into every profession, including the oldest."

In a recent case eight women were arrested on prostitution charges after just such a police sting operation.

Meanwhile, other police are finding the site very useful in similar cases as more prostitutes go online. Illinois police arrested 43 prostitutes on the street in July, compared to 60 found online.

Police are also using the site to catch those who buy sex. A single advert in the Seattle section of Craigslist netted 71 respondents, including a bank officer, a construction worker and a surgeon.