Meta and Google teamed up to run a secret campaign that deliberately targeted 13 to 17-year-olds with Instagram ads on YouTube according to the Financial Times, breaking the search giant’s own rules against advertising to children.

The publication reports that Google directed ads to a subset of users labeled as “unknown” in its advertising systems, in an attempt to disguise the group skewed toward teenagers. According to a Google Ads help page, the “unknown” demographic category refers to people whose age, gender, parental status, or household income are supposedly unidentified, and can allow advertisers to reach “a significantly wider audience” when selected.

However, Google could use app downloads and online activity to determine “with a high degree of confidence” that the “unknown” group was populated by younger users, reports the FT. Google staffers are said to have used this loophole to get around the company’s own policies, having introduced rules that block ad targeting based on “age, gender, or interests of people under 18” back in 2021.

Spark Foundry, a US-based subsidiary of the ad giant Publicis, reportedly worked with the companies to launch the illicit marketing campaign in Canada between February and April this year, before going on to trial the program in the US in May. Meta and Google intended to expand the campaign to international markets and promote additional services like Facebook, according to the FT. The program was initiated amid a decline in Google’s advertising earnings and the migration of Meta’s younger users to rival services like TikTok.

Google has since launched an investigation into the allegations, and the campaign has now been canceled, the FT reports. “We prohibit ads being personalized to people under-18, period,” Google said in a statement to the publication. “We’ll also be taking additional action to reinforce with sales representatives that they must not help advertisers or agencies run campaigns attempting to work around our policies.”