After four weeks, about 80 percent of the fake clicks remained, the researchers said. And virtually all of the accounts that had been used to generate the clicks remained active three weeks after researchers reported them to the companies.

Image Researchers inflated the “likes” on a Facebook post by Margrethe Vestager, Europe’s top antitrust enforcer.

The report spotlights the continuing challenges for Facebook, YouTube and Twitter as they try to combat online disinformation and other forms of online manipulation. After Russia interfered in the United States’ 2016 presidential election, the companies made numerous changes to reduce the spread of online disinformation and foreign interference. In recent months, the platforms have announced takedowns of accounts in China, Saudi Arabia and, most recently, Africa, where Russia was testing new tactics.

But the report also brings renewed attention to an often overlooked vulnerability for internet platforms: companies that sell clicks, likes and comments on social media networks. Many of the companies are in Russia, according to the researchers. Because the social networks’ software ranks posts in part by the amount of engagement they generate, the paid activity can lead to more prominent positions.

“We spend so much time thinking about how to regulate the social media companies — but not so much about how to regulate the social media manipulation industry,” said Sebastian Bay, one of the researchers who worked on the report. “We need to consider if this is something which should be allowed but, perhaps more, to be very aware that this is so widely available.”