Bismillah writes: The recent 13-microsecond timing anomaly was caused by a satellite failure triggering a "software issue", the USAF 50th Space Wing has confirmed. Such an error is large enough to cause navigation errors of up to 4 km. Luckily, no issues with GPS guided munition were reported. Reader donaggie03 adds a link to the official explanation from Rick Hamilton, Executive Secretariat of the Civil Global Positioning System Service Interface Committee. From Hamilton's email: Further investigation revealed an issue in the Global Positioning System ground software which only affected the time on legacy L-band signals. This change occurred when the oldest vehicle, SVN 23, was removed from the constellation. While the core navigation systems were working normally, the coordinated universal time timing signal was off by 13 microseconds which exceeded the design specifications. The issue was resolved at 6:10 a.m. MST, however global users may have experienced GPS timing issues for several hours.