Cybercrime specialists from Germany, the United States, and Canada have dismantled two of the world’s largest botnets, Aisuru and Kimwolf, believed to be responsible for major online attacks.

Authorities announced on Friday that the coordinated international operation successfully shut down the massive bot networks.

They said the networks “posed a significant threat to IT infrastructure due to their size and associated attack capacity,” according to German police, prosecutors, and cybercrime authorities.

A botnet is a network of computers or connected devices infected with malware and covertly controlled by an operator, who uses them to carry out malicious activities such as cyberattacks or data theft.

Aisuru was made up of a network of several million compromised internet-connected devices, including routers and webcams, according to a statement.

The second botnet, known as Kimwolf, was linked to several million infected devices, mainly Android TV boxes.

Two suspected administrators of the networks have been identified and now face “legal consequences,” the statement said, though no further details were provided.

The botnets carried out so-called “distributed denial-of-service attacks,” in which operators overwhelm compromised devices with huge volumes of traffic to slow them down or shut them off entirely.

According to the U.S. Department of Justice, which participated in the operation, the networks were responsible for “record-breaking attacks.”

Officials said infected devices were effectively “enslaved” by the operators, who then sold access to the compromised systems to other cybercriminals.