Also see Google summoned to appear before the UK government to explain why ads keep appearing next to extremist YouTube videos (Business Insider)
"Ads for the Guardian’s membership scheme are understood to have been placed alongside a range of extremist material after an agency acting on the media group’s behalf used Google’s AdX ad exchange.
David Pemsel, the Guardian’s chief executive, wrote to Google to say that it was “completely unacceptable” for its advertising to be misused in this way.
He said the Guardian would be withdrawing its advertising until Google can “provide guarantees that this ad misplacement via Google and YouTube will not happen in the future”.
The content included YouTube videos of American white nationalists, a hate preacher banned in the UK and a controversial Islamist preacher."Guardian pulls ads from Google after they were placed next to extremist material | Media | The Guardian