If you live in the Sacramento area and experienced shoddy Internet service yesterday, there’s a chance it wasn’t your provider’s fault. Federal investigators say someone has been attacking high-capacity Internet cables for a least a year, with the most recent attack occurring on Tuesday.

USA Today reports (warning: link has video that autoplays) that the FBI is investigating at least 11 physical attacks on Internet cables around Sacramento and the San Francisco Bay area, some of the assaults dating back at least a year.

The latest issue occurred in the early hours of June 30 around Sacramento, disrupting service for businesses and residential customers.

According to FBI agents – who declined to say just how much the latest attack affected customers – someone broke into an underground vault and cut three fiber-optic cables belonging to service providers Level 3 and Zayo.

A spokesperson for Wave Broadband, which connects to the affected service providers, confirmed to USA Today that the latest cord-cutting situation impacted an unspecified number of customers in the Sacramento-area. The company characterized the attack as “coordinated,” and is working with Level 3 and Zayo to restore service.

JJ Thompson, CEO of Rook Security, a security consulting and services provider in Indianapolis, tells USA Today that the attacks showcase the vulnerability of Internet infrastructure.

While fiber-optic cables are often bundles of thin cords, they are generally protected by strong, flexible conduit, meaning cutting the lines would require tools and planning.

“When it’s situations that are scattered all in one geography, that raises the possibility that they are testing out capabilities, response times and impact,” Thompson said. “That is a security person’s nightmare.”

USA Today reports that backup systems in the area helped lessen the significance of the attack on Tuesday. Many people may have noticed slower email or issues with videos loading, but overall service may not have been completely disrupted.

“When it affects multiple companies and cities, it does become disturbing,” an agent tells USA Today, adding that the first known attack occurred in July 2014. “We definitely need the public’s assistance.”

FBI investigating 11 attacks on San Francisco-area Internet lines [USA Today]

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