The duo focused on the 180 fashion and luxury ads 43 of which led to websites selling counterfeit goods.

"You do not know where you are going to end up. In many cases, your credit card is at risk, thanks to obscure payment systems backed by companies you have no idea who they are," researchers Andrea Stroppa and Agostino Specchiarello said.

The websites often had legitimate looking URLs and even have fake logos of security and payment system companies, researchers found. According to them, since they started the study, many of such ads have been removed.

Reacting to this, a Facebook spokesperson said, "We prohibit fraudulent or misleading claims or content, and to enforce our terms and policies, we have invested significant resources in developing a robust advertising review programme that includes both automated and manual review of ads".