A previously undisclosed cyberattack launched in late 2023 crippled hundreds of thousands of internet routers across the U.S. heartland, according to a report published by security researchers at Lumen Technologies.

The attack, which targeted an unnamed telecommunications company, took place in October and left many residents in Midwestern states without internet access for several days. Researchers believe it to be one of the most significant cyberattacks ever against the American telecommunications sector.

The attackers reportedly infiltrated the company’s system and installed malicious software that disabled internet routers. This software remained undetected for months, raising concerns about ongoing vulnerabilities.

While the specific company remains unidentified, details in the report suggest Arkansas-based internet service provider Windstream may have been the target. Windstream declined to comment on the matter.

The attack had potentially severe consequences, particularly in rural areas where residents rely on internet access for emergency services, agricultural monitoring, and healthcare.

The report highlights the growing threat of cyberattacks on critical infrastructure and the need for improved cybersecurity measures.

The FBI’s involvement in the investigation remains unclear, as private companies often choose not to disclose such incidents.