They found more than 8,000 ads for these lists on Craigslist, and said the service flagged only 57 percent of them.
Overall, Craiglist failed to flag 47 percent of the rental ads that were probably scams, and for those that it did identify, it took a long time to flag them.
Of the listings cloned from other real estate websites, 60 percent stayed up for 10 hours, and 40 percent remained online for more than 20 hours -- plenty of time to catch some victims.
McCoy, who also co-authored a paper on another type of Craigslist scam, said the researchers reached out to Craigslist but received no response.
"It'd be great to work with them and try to improve the situation," he said.
The study's other authors were Youngsam Park of the University of Maryland and Elaine Shi of Cornell University.
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