Russia has entirely banned Pornhub and ten other similar websites because they are harmful to children.

The ban was announced in Monday and now seems to have gone into effect, with visitors just seeing a message telling them that it had been banned “for containing unlawful content”, according to the Moscow Times.

Courts haven’t said precisely what content led them to block access to the sites. The court orders that led to them being taken down only said that they contained “pornographic material prohibited by the law (images, videos, movies)”, according to Russian site Lenta.

The courts made reference to PornHub being harmful to the health and development of children, according to the Russian news site. It wasn’t clear whether that was because children are using the sites, or if it was because they were being accused of hosting child abuse content.

Russia’s regulators have blocked a range of huge US sites in recent weeks. Recently, it blocked both Reddit and Wikipedia because of individual pages about drugs, though those blocks were lifted once the sites made Russia’s requested changes.

The reasoning behind the bans is almost identical to David Cameron’s arguments for shutting down porn websites in the UK. In July, he said that sites would be forced to put stringent age checks in place or the sites would be banned.