Revelation found in files obtained by the American Civil Liberties Union
The sites 'advertised' and 'discussed' child pornography, documents say
An FBI spokesman denied knowing about the 23 websites in question
The FBI reportedly operated almost two dozen child pornography websites hidden on the dark web to lure and catch predators.
Unsealed documents obtained by the American Civil Liberties Union revealed investigators had the authorization to run 23 such websites.
It had already been known that the agency ran the website, Playpen, to help identify users.