Hackers specialize in collecting card data and then sell it in the forums to other fraudsters, who try to buy goods online or create fake cards in an attempt to cash out.

CloudeyeZ is monitoring more than 300,000 sets of card details, which mostly are U.S. cards including Visa, MasterCard, Discover and American Express. Visa cards appear to be the most popular, which CloudeyeZ attributes to the large number of cards in circulation, which has also made those the cheapest cards at around $2 each.

The project has only been running for about three weeks, so it is too early to spot trends. But CloudeyeZ hopes the monitoring will reveal factors that influence prices, such as law enforcement actions, Clements said.