It started as a cheeky response on social media to the US secretary for homeland security. Months later, however, a Europe-based project to unmask US immigration and custom enforcement (ICE) agents has racked up millions of views and mobilised hundreds of volunteers.

“What we’re doing is a reaction to a problematic regime,” said Dominick Skinner, the Netherlands-based Irish national behind the website ICE List, of its mission to remove the anonymity that many of the armed federal agents operate under while deployed to US cities.

The roots of the website trace back to June, when Kristi Noem, the US homeland security secretary, warned that Americans who identified ICE agents publicly would face arrest. “I reposted that and said, ‘well, we’re not in the US, so send them to us,’” said Skinner, 31. “By the evening I had private investigators messaging me, and by the next week we had a framework of how to work.”

The site currently operates as a sort of crowdsourced wiki, drawing on a pool of about 500 volunteers to comb through tips from the public. As tensions swirl over ICE’s presence on US streets, another 300 people have expressed interest in volunteering, he says.