(LONDON) — Social media companies are failing to stop manipulated activity, according to a report Friday by NATO-affiliated researchers who said they were easily able to buy tens of thousands of likes, comments and views on Facebook, Twitter, YouTube and Instagram. Most of the phony accounts and the activity they engaged in remained online weeks later, even after researchers at the NATO Strategic Command Centre of Excellence flagged them up as fake. The center, an independent group based in Latvia that advises the military alliance, said the findings contrast with statements from tech companies that say they’ve been working harder on stamping out manipulation. “Overall social media companies are experiencing significant challenges in countering the malicious use of their platforms,” the report said. Online manipulation emerged as a major issue for tech companies after the 2016 U.S.