He was a member of a band in Niterói, a city in Brazil surrounded by beaches, and he honed his guitar skills by watching tutorials online. YouTube had recently implemented a new artificial intelligence system that analyzed user behavior to suggest videos, leading him to discover a popular amateur guitar teacher named Nando Moura, known for his videos on heavy metal, video games, and politics. Moura's far-right conspiracy theories captivated him, and as he spent more time on the platform, he was recommended videos from other far-right personalities, including then-lawmaker Jair Bolsonaro. YouTube played a significant role in shaping his political views to the far right, and he now aspires to enter politics himself. YouTube has built its success by engaging users, but this has inadvertently benefited extremist groups. An investigation in Brazil, the company's second-largest market, revealed serious repercussions. The far-right movement in the country credits YouTube's recommendation system for their rapid rise to power. Recent studies support this claim, showing that the platform's algorithms have consistently directed users towards far-right and conspiracy content. The New York Times' investigation in Brazil uncovered how these promoted videos have disrupted everyday life, leading to unruly classrooms, misinformation on health issues, and other harmful consequences. Viral videos have led to death threats against public health advocates, while right-wing YouTube stars have joined politics and use the platform for trolling and provocation. YouTube's recommendation system is designed to keep users watching by suggesting videos that may include extreme content, leading to concerns about radicalization. Despite the platform's denial, some experts believe YouTube is a powerful tool for radicalization in the 21st century. Nevertheless, representatives from the company acknowledged some of the conclusions and assured that changes would be made. Farshad Shadloo, a spokesperson, stated that YouTube had made significant investments in policies, resources, and products to combat the spread of harmful misinformation, noting that authoritative content is thriving in Brazil and is highly recommended on the platform. Danah Boyd, founder of the think tank Data & Society, linked the disruption in Brazil to YouTube's relentless drive for viewer engagement and revenue generation. Despite the country already facing corruption scandals and a severe recession, Boyd expressed concern over YouTube's growing influence on democracies worldwide. Maurício Martins, the local vice president of Bolsonaro's party in Niterói, attributed most of the party's recruitment to YouTube, including his own. He described how YouTube auto-playing recommendations served as his political education, a sentiment echoed by many others. The platform's political impact is increasingly apparent in Brazilian schools, with students citing YouTube stars as their main source of information. Carlos Jordy, a City Council member, exemplifies YouTube's influence as he transitioned from traditional politics to focus on YouTube, posting videos accusing local teachers of promoting communism. He stated that his videos gained him a wide audience nationwide and helped him quickly rise to the federal legislature two years later. He credited social media for his success, stating that without it, neither he nor Jair Bolsonaro would be in their respective positions. Researchers at the Federal University of Minas Gerais analyzed YouTube videos and comments, finding that right-wing channels in Brazil were growing faster and influencing the site's political content. Positive mentions of Bolsonaro increased after YouTube changed its algorithm, even though polls still showed him to be unpopular. A team at Harvard's Berkman Klein Center investigated whether YouTube's recommendation engine had contributed to the far right's rapid growth in Brazil. They programmed a server to explore popular channels and search terms on YouTube, tracking how the platform guided users from one video to the next. They discovered that following the viewing of a video related to politics or entertainment, YouTube tended to recommend right-wing, conspiracy-driven channels like Moura's to users. Importantly, users who watched one extreme right channel were often recommended many more. The researchers found that the algorithm had brought together previously marginalized channels and helped them build a larger audience. One of these channels belonged to Bolsonaro, who had been using the platform to share hoaxes and conspiracy theories. Despite being an early adopter of YouTube, his online following had not significantly expanded his political base, which was minimal at a national level. However, when Brazil's political system collapsed and YouTube's popularity surged, Bolsonaro's far-right content, where he was a prominent figure, gained a massive audience, effectively preparing many Brazilians for his message during a time of political transformation. YouTube disputed the researchers' methods and claimed that their internal data contradicted the findings, but they refused to provide the data or statistics requested by the Times to verify the accuracy of the researchers' conclusions. The spread of conspiracies was not limited to politics. Numerous Brazilians who turned to YouTube for health information were frightened by videos claiming that Zika was being spread by vaccines or insecticides meant to control the disease. These videos, similar to extremist political content, made alarming claims and promised hidden truths that captivated viewers. As a result, many frightened patients refused vaccines and insecticides, leading to a public health crisis in communities like Maceió. Doctors and health workers struggled to combat the misinformation spread by these videos, as patients increasingly chose to believe what they found online over medical advice. This has led to a resurgence of Zika in some areas, as more communities reject larvicides. The medical community in Brazil feels overwhelmed by the influence of social media on public health decisions. Harvard researchers discovered that YouTube's algorithms often directed users searching for information on Zika or watching reputable health videos towards conspiracy channels. A YouTube spokesperson acknowledged the unintended findings and pledged to adjust the search tool to display Zika-related videos differently. The rise of the far right enabled conspiracy videos to be weaponized, with leading voices targeting individuals like women's rights activist Debora Diniz. YouTube stars, such as Bernardo Küster, accused Diniz of involvement in supposed Zika plots, suggesting that those working to help Zika-affected families were actually behind the disease. As far-right and conspiracy channels began referencing each other, YouTube's recommendation system began linking their videos, creating the illusion of widespread consensus on unfounded rumors. Diniz faced threats of rape and torture as a result of these conspiracy theories. Diniz stated that Küster's videos contained numerous repeated claims, and although Küster never explicitly supported the threats mentioned in the videos, he managed to stay within YouTube's guidelines. When Diniz's university received a warning of a potential shooting targeting her and her students, and the police could no longer guarantee their safety, she decided to leave Brazil. Diniz criticized the YouTube recommendation system for creating a culture of hate, where viewers are exposed to harmful narratives about individuals and groups. She emphasized the importance of holding companies accountable for their role in propagating hate speech. They are considered to be ethically accountable. On YouTube, there is a trend of spreading conspiracies targeting aid groups involved in controversial issues like abortion. This trend, known as "linchamento" in Brazil, has caused even long-time supporters of these groups to question the accuracy of the videos and avoid them. Bolsonaro was one of the first to spread false accusations in videos, leading to a culture of hate and fear. Jordy, a follower of Bolsonaro, had no remorse for the fear caused by his YouTube campaign. He believed it was necessary to fight a culture war and was his purpose in coming into office. The São Paulo headquarters of Movimento Brasil Livre is seen as the epicenter of political influence through YouTube. The group's members are typically young, middle-class, right-wing, and heavily involved in online activities. Renan Santos, the national coordinator, pointed to a door labeled "the YouTube Division" as the central hub of the group. Inside, a group of young men were working on editing software, including creating an image of Benito Mussolini for a video arguing that fascism was wrongly associated with the right. Despite their dedication to social media, some members expressed concerns about its impact on democracy. The co-founder, Pedro D'Eyrot, referred to social media as the "dictatorship of the like," emphasizing how viral messages shape reality. A controversial YouTube video titled "1964" was influencing public opinion by arguing that Brazil's military coup was necessary to prevent communism. This video convinced some viewers, like teenager Dominguez, that his teachers had distorted the truth about military rule. However, others, like history teacher Borges, were reminded of the dark memories of military rule, including curfews, disappeared activists, and police violence. Despite the divisive impact of social media, individuals like Matheus Dominguez credited YouTube for leading them to adopt far-right political views. YouTube has established its success by ensuring that users remain engaged, which has inadvertently benefitted extremist groups. A study conducted in the company's second-largest market uncovered significant repercussions. (Dado Galdieri/The New York Times)