NATO-affiliated researchers say social media companies are failing to stop manipulated activity.

They show in a report how they were easily able to buy thousands of likes, comments and views on Facebook, Twitter, YouTube and Instagram.

The researchers said Friday's report that most of the phony accounts and posts remained online weeks later, even after they flagged them up as fake.

The findings contrast with statements from major tech companies.

They say that they have been working harder on stamping out manipulation including removing fake accounts and preventing artificial video views.

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