The photo-sharing website Imgur, best known as the origin point for many of the Internet's viral GIFs, has been exploited to launch a cyberattack against the image boards 4Chan and 8Chan. The distributed-denial-of-service attack overwhlemed 4Chan and 8Chan with traffic, destabilizing the popular sites and slowing them to a crawl.

Imgur announced on its website Tuesday that an unknown hacker or group of hackers had uploaded a malicious HTML file to Imgur that targeted all users of the 4Chan and 8Chan discussion threads on Reddit, a major source of traffic for 4Chan and 8Chan. In effect, when a user clicked a single link to 4Chan or 8Chan in that sub-Reddit, that link would trigger hundreds of other invisible windows.

Hackers frequently use DDoS attacks to cripple target websites, or knock them offline entirely. The method has been used most frequently by the hacker group Anonymous and, more recently, by the Chinese government to silence critical websites hosted in the United States. Who was behind the Imgur DDoS and what motivated them remains unclear.

“The affected images were not published to the galleries on Imgur.com,” Imgur wrote in the post Tuesday. “The vulnerability was patched yesterday evening, and we're no longer serving affected images, but as a precaution we recommend that you clear your browsing data, cookies and local storage.”

4Chan is best known for hosting the /b/ forum, a dark corner of the Internet where the Anonymous collective originated and nude celebrity photos later published as part of "The Fappening" scandal last year. The community-based image board was sold this week to the founder of the Japanese Internet culture site, 2Channel. 

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