The OurMine hackers known for hijacking online social media accounts, supposedly to test their security, executed what it's calling the largest hack in YouTube history, after changing the written content on hundreds of the video service's channels on Friday.

According to various media reports, including one from the Sydney Morning Herald, OurMine temporarily seized control of the YouTube account belonging to German media network Studio71, which hosts over 1,200 channels, including RomanAtwoodVlogs, JustKiddingNews and Wranglerstar. The group altered the titles and descriptions of the affected videos to "Hey, it's OurMine, don't worry we are just testing your security, please contact us for more information."

In the last year, OurMine has claimed responsibility for hacking the social networking accounts of Britney Spears, Mark Zuckerberg, the New York Times and other prominent celebrities and media and entertainment companies.

YouTube is a subsidiary of Google.