On December 3, tens of thousands of residents in North Carolina experienced a massive power loss. But it was no accident. Attackers had rained gunfire on two facilities that regulate the power grid and knocked them out of operation. It took days to bring everything back online.

These attacks weren’t an anomaly. An Insider investigation found strikes against the electrical grid nationwide to be at an all-time high — and experts say the biggest threat comes from right-wing extremists looking to dissolve social order.

Insider analyzed new data, visited electrical substations, reviewed law-enforcement records and neo-Nazi propaganda, and interviewed several experts. The report reveals that while attacks against the grid are up, efforts to protect it are lagging, and perpetrators are rarely caught — leaving huge swaths of America’s electrical infrastructure vulnerable.