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GitHub is struggling to contain an ongoing attack that’s flooding the site with millions of code repositories. These repositories contain obfuscated malware that steals passwords and cryptocurrency from developer devices, researchers said.

The malicious repositories are clones of legitimate ones, making them hard to distinguish to the casual eye. An unknown party has automated a process that forks legitimate repositories, meaning the source code is copied so developers can use it in an independent project that builds on the original one. The result is millions of forks with names identical to the original one that add a payload that’s wrapped under seven layers of obfuscation. To make matters worse, some people, unaware of the malice of these imitators, are forking the forks, which adds to the flood.

Whack-a-mole

“Most of the forked repos are quickly removed by GitHub, which identifies the automation,” Matan Giladi and Gil David, researchers at security firm Apiiro, wrote Wednesday. “However, the automation detection seems to miss many repos, and the ones that were uploaded manually survive. Because the whole attack chain seems to be mostly automated on a large scale, the 1% that survive still amount to thousands of malicious repos.”