The British Police Intellectual Property Crime Unit (PIPCU) has started to replace advertising on copyright-infringing websites with official warnings telling users that the site is under criminal investigation.

The sites in question are those that have been identified as hosting copyright-infringing content and reported to PIPCU by rights holders. Officers from the unit evaluate the sites to verify that they are infringing copyright. They then contact the site owner to give them the opportunity to "correct their behavior" and operate legitimately. If that fails, PIPCU can get the site taken down by contacting the domain registrar, replacing the site's ads with the scary warnings, or adding the sites to the infringing website list. When a site is added to that list, the information is fed back to a group of 60 marketing agencies, advertising technology companies, and brands responsible for placing ads, and they are then asked to stop placing ads on those sites.

In order to get PIPCU's banners onto the copyright infringing sites, the police have partnered with content verification company Project Sunblock. Project Sunblock maintains the list of infringing websites and then makes sure that when clients' advertisements are going to be delivered to one of those sites, the police banners are served as a replacement. Neither Project Sunblock nor the police pay for this ad placement; they simply serve an alternative ad. Project Sunblock then reports back to the client which ads have been blocked and on how many occasions.

This approach has been adopted after many big brands were found to be advertising on sites hosting pirated content. These sites tend to place their ad inventory into ad networks and exchanges to generate revenue from the audiences they attract, so well-respected brands inadvertently find themselves "sponsoring" piracy.

During a pilot last year, the number of ads from well-known brands on these websites fell by 12 percent.

This is the latest phase of Operation Creative, an initiative—launched in partnership between the police and the creative industries—that aims to disrupt online piracy by targeting those sites that host infringing content.

Head of PIPCU Andy Fyfe said that copyright-infringing websites are making "huge sums of money" through ad placement, so disrupting advertising on these sites "is crucial."

"This work also helps us to protect consumers. When adverts from well-known brands appear on illegal websites, they lend them a look of legitimacy and inadvertently fool consumers into thinking the site is authentic," he added.

This story originally appeared on Wired UK.