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.