The betting industry says it takes under 30 seconds to sign up to a black market site compared to 12 minutes for a regulated UK operator.
It comes as ministers prepare to publish a gambling white paper.
Michael Dugher, CEO at the Betting and Gaming Council, said punters face a “dire threat” from “the growing unsafe, unregulated black market”.
He said the regulated industry worked hard to protect young people during the World Cup by adhering to strict regulations while black market operators “preyed on the vulnerable”.
He added: “While the regulated industry was going to great lengths to protect young people during the World Cup and adhering to strict regulations and promoting safer gambling, black market operators were preying on the vulnerable.
“These unlicensed sites offer none of the safer gambling tools promoted by our members, they pay no tax and employ no one, they do not contribute a penny to sport or services tackling gambling harm.
“Rather than dismissing the problem, the regulator and the Government need to tread extremely carefully and resist blanket intrusive affordability checks at low levels that push even more punters to these dangerous sites.”
He praised the research by Yield Sec, a US-based licensed gaming marketplace.