The Federal Bureau of Investigation moved to dismantle a large network of hacked routers and storage devices that Cisco Systems Inc. and U.S. and Ukraine authorities said could be used to launch a massive cyberattack or knock hundreds of thousands of internet users offline.
The FBI said late Wednesday that it has seized control of the internet domain that was used by the computer network’s “command and control” server to issue instructions to infected devices. The agency said it has begun an effort to clean up the estimated...