On the internet, an advert that appears next to a YouTube video earns money regardless of the content of the video — this can range from US$5 to US$8.01 for every 1000 views, London newspaper The Times has revealed.
According to an investigation carried out by the newspaper, advertisements for firms including Mercedes-Benz and supermarket chain Waitrose, as well as cancer charity Marie Curie, were showing up online next to videos posted by extremist groups.
Following the revelation that a Marie Curie advert appeared alongside a Combat 18 video, the charity released a statement.
"We are extremely concerned that our advertising has appeared in this way. We are investigating how this has happened and will take what further steps necessary to ensure this does not happen again," the statement read.
In another example, an online advert for car company Mercedes was found to be on a pro-Daesh video and viewed 115,000 times, The Times reported.
The advertisers said they were "deeply concerned," but denied any wrongdoing.
Google, which owns YouTube said it has a "zero-tolerance policy for content that incites violence and hatred."