 Seventeen major flares erupted on the Sun between 19 October and 5 November 2003, including perhaps the most intense flare ever measured on the GOES XRS sensor—a huge X28 flare, resulting in an extreme radio blackout, on 4 November.These flares were associated with CME events that caused three geomagnetic storms between 29 October and 2 November, during which the second and third storms were initiated before the previous storm period had fully recovered.The minimum Dst values were −151, −353 and −383 nT.