Hackers on Friday made good on their threat to take down the 2014 World Cup site in Brazil.

Anonymous, the loose hacker collective, appears to have successfully taken down the site, which was offline for several hours Friday evening. The hacker group Anonymous Brasil has started a hacking campaign — Operation Hacking Cup, or #OpHackingCup — to protest poverty, corruption and police brutality.

Offline, activists have struggled to make their voices heard, but online, hackers have begun a series of distributed denial-of-service, or DDoS, attacks and have defaced websites.

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In one tweet, the group claims to have started more than 100 attacks since the World Cup began. Their targets have included the Brazilian Intelligence System, Hyundai Brazil, the Brazilian Football Confederation, Brazil’s Justice Department, the Sao Paulo military police, Bank of Brazil and the Africa.com.br website.

This week, the group claimed to have hacked the internal servers of the Brazilian federal police. As proof, the group released a collection of user names and passwords and a link to the federal police’s internal log-in site, but the authenticity of the information could not be verified.

Security experts say that they are not surprised. DDoS attacks typically involve hackers using networks of infected computers, called botnets, to fire traffic simultaneously at their victim until the site collapses. And these days, experts say, even a teenager can pull off a successful DDoS attack.

“In a time when anyone can Google up a ‘botnet for hire’ and use it to execute a 20-to-40-gigabits-per-second attack, from several thousands sources, no threat can be truly dismissed,” said Igal Zeifman of Incapsula, a DDoS mitigation service.

Anonymous has also threatened to hack World Cup sponsors, including Adidas, Budweiser, Coca-Cola and Emirates Airline. But so far, only Brazilian sites appear to have been affected.