AT&T Network Collapse from Code Bug

On January 15, 1990, AT&T's long-distance network collapsed nationwide after a software update introduced a faulty break statement in a C routine. This flawed logic caused switches to misinterpret "reset" and "recovery" messages, triggering cascading shutdowns across its 114 4ESS switching systems. The outage lasted roughly 9 hours, disrupted tens of thousands of calls, grounded flights, and cost the company an estimated $60 million in losses.

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