The incident occurred on the same day as coordinated cyberattacks struck more than 30 other renewable energy installations and a larger heat plant, as Poland publicly disclosed in January. The analysis, which took more than three months, uncovered what the agency described as the first known use of a private cellular data network as a pathway into an industrial control system. Wind farms and other distributed energy sites communicate with grid operators through private cellular networks; dedicated mobile data connections the industry treats as secure, walled-off infrastructure. The entire chain — wind farm to cellular network to heat plant — saw the hackers move across facilities with no direct relationship to one another besides their shared presence on the same private network. The agency is urging energy operators to stop treating private cellular networks as trusted infrastructure and to apply the same controls they would use for any internet-facing connections.