The FBI is investigating the severing Tuesday of a cluster of high-capacity fiber-optic cables in the Bay Area that disrupted phone and cable service and slowed Internet access to customers in Northern California.

A vandal was believed to have entered an Alameda County manhole and clipped three fiber-optic cables housed in a subterranean vault. It was the latest in nearly a dozen such attacks during the past year across the Bay Area, FBI spokesman Greg Wuthrich said.

The attack highlighted the vulnerabilities and interconnectivity of the telecommunications grid. Homes, businesses and Internet service providers across Northern California were frustrated by the severed lines.

“Pretty much everybody who has a large network in the Bay Area” was affected by the vandalism, said Peter Kranz, chief executive of Berkeley-based Internet provider Unwired Ltd. “The fiber bundles carry traffic for lots and lots of companies. Hundreds, thousands of businesses will share.”

The effect of the damage on area businesses and customers was not fully known, Wuthrich said.

Service since has been fully restored, the companies announced Tuesday night and Wednesday.

At least two companies acknowledged that fiber-optic cables they own were compromised in the attack. The Colorado-based firms Level 3 Communications and Zayo Group have fiber lines used by Wave Broadband, whose customers stretch from Silicon Valley to the U.S.-Canadian border.

Wave Broadband spokesman Mark Peterson said the severed cable lines primarily affected customers in suburban areas around Sacramento and Rocklin, Calif.

Customers were expected to have slow Internet service and partial TV service. Phone service also was being restored, Peterson said.

“It’s a huge inconvenience, but it’s not a comprehensive outage,” said Peterson, who could not provide the number of customers affected.


Kranz said he was alerted to the clipped lines shortly after 4:20 a.m. His company was able to reroute traffic, but the drop in available routes “stressed the network,” he said.

Microsoft general manager Adrienne Hall acknowledged in a statement that service was rerouted for customers because of issues related to a cut cable, but Hall did not pinpoint the location.

A bundle of fiber-optic lines also was cut in the Portland, Ore., area, which further disrupted service to Level 3, according to a company statement. The company said the two incidents were unrelated.

Since July 6, 2014, fiber-optic cable lines have been intentionally severed in at least 10 Bay Area cities, including Fremont, Berkeley, San Jose and Walnut Creek, according to the FBI.

Investigators are unsure how — or if — the incidents are connected. The nature of the attacks, often in remote areas, perhaps by vandals dressed as utility workers, has made it difficult to identify suspects, Wuthrich said.

“Different companies have thousands of these vaults,” he said.

Attacks on the telecommunication infrastructure are not new.

Fiber-optic cables at four California locations were clipped April 9, 2009, shutting down service for more than 50,000 people in Santa Clara, Santa Cruz and San Benito counties, the San Francisco Chronicle reported.

On April 16, 2013, suspects clipped fiber-optic cables outside San Jose before snipers opened fire on electrical transformers at PG&E’s Metcalf Transmission Substation, causing more than $15 million in damage.

According to the FBI, the recent spate of fiber cuts are unconnected to the sniper attack on the Metcalf substation. No one has been arrested in connection with that attack.

Anyone with information about the vandalism is asked to contact the FBI at (415) 553-7400.

For breaking news in California, follow @MattHjourno.