Natural disaster
A solar flare is a phenomenon where the Sun suddenly releases a great amount of solar radiation, much more than normal. Solar flares are unlikely to cause any direct injury, but can destroy electrical equipment. The potential of solar storms to cause disaster was seen during the 1859 Carrington event, which disrupted the telegraph network, and the March 1989 geomagnetic storm which blacked out Quebec. Some major known solar flares include the X20 event on August 16, 1989, and a similar flare on April 2, 2001. The most powerful flare ever recorded occurred on November 4, 2003 (estimated at between X40 and X45).
Solar cycle 24
A filament eruption occurred in late hours of September 27 resulted in a brief S1 (minor) radiation storm, alerted by NOAA in early hours of next day. The Earth-directed CME associated with this event affected our planet on September 30. Geomagnetic storm levels reached the G3 on October 1. The filament eruption was connected to a C3.7 flare occurred in the vicinity of sunspot 1577.
Solar activity decreased remarkably this month. 4 minor solar flares, below M2 levels, were registered in September 2012.
On October 8 and 9, the arrival of a CME unrelated to solar flares and emitted on October 5 caused disturbances in the horizontal component of the Earth's magnetic field. The planetary Kp-index reached level 6, so a G2 (moderate) geomagnetic storm was reported. 
The Sun released a M9.0 flare on October 20. This was followed three days after on October 23, by a very impulsive flare, peaking as an X1.8 class event at 3:17 a.m. UTC. 
Both flares came from active region 1598 located on the left side (east) of the sun, which had previously been the source of a number of weaker flares. The M9.0 burst occurred when the sunspot was not yet rotated onto the Earth-facing side of the solar disk. The NOAA categorized the radio blackout associated with the X1.8 event as an R3, on a scale from R1 to R5. This was the 7th and last X-class flare in 2012. There was no associated Earth-directed coronal mass ejection (CME).