Recent studies find that a large solar eruption in 2012 could have fried vast swaths of electronic systems worldwide  if it had impacted the earth:

From the NASA Science article:

Before July 2012, when researchers talked about extreme solar storms their touchstone was the iconic Carrington Event of Sept. 1859, named after English astronomer Richard Carrington who actually saw the instigating flare with his own eyes.  In the days that followed his observation, a series of powerful CMEs hit Earth head-on with a potency not felt before or since.  Intense geomagnetic storms ignited Northern Lights as far south as Cuba and caused global telegraph lines to spark, setting fire to some telegraph offices and thus disabling the ‘Victorian Internet.”

A similar storm today could have a catastrophic effect. According to a study by the National Academy of Sciences, the total economic impact could exceed $2 trillion or 20 times greater than the costs of a Hurricane Katrina. Multi-ton transformers damaged by such a storm might take years to repair.

“In my view the July 2012 storm was in all respects at least as strong as the 1859 Carrington event,” says Baker. “The only difference is, it missed.”

Keep an eye on the sun at HobbySpace Sun & Space Weather page.