Any time a carrier has an outage that affects 900,000 caller minutes–say a 30-minute outage impacting 30,000 customers–it must report it to the Network Outage Reporting System. In the beginning, the reports all were from “wire line” telephone providers and were available to the public. But in 2004, the commission ordered wireless firms to supply outage reports as well. But at the same time, it removed all outage reports from public view and exempted them from the Freedom of Information Act. The FCC took the action at the urging of the Department of Homeland Security, which argued that publication of the reports would “jeopardize our security efforts.”
As Amanda puts it:
It’s unclear how terrorists would use this information; perhaps with an appeal to the same magic force that would let them use an ounce of shampoo in an 8-ounce bottle to take down an airplane. But it sure is clear how this policy benefits the cellular companies.
Relatedly, Bram Cohen quotes a friend who says that information about power grid outages are no longer published for the same reason.