Rachel Nuwer for BBC - Future:

The most devastating strikes could come from space, however. A large solar storm that sent flares in our direction would take out satellites, power grids and computer systems. “What bombs and terrorism can’t do might be accomplished in moments by a solar flare,” says David Eagleman, a neuroscientist at Stanford University and author of Why the Net Matters. “The next major geomagnetic storms are eventually coming.”

But most outages would not last long. “There’s an army of people ready to put things right,” says Scott Borg at the United States Cyber Consequences Unit, a non-profit organisation. “The internet service providers and the companies that make the routing equipment have plans and personnel in place for getting things up and running again if unexpected vulnerabilities are exploited.” We are so used to having an always-on internet connection that even relatively short disruptions would have an effect, however. It just might not be what you would expect.

For a start, the impact to the economy may not be too severe. In 2008, the US Department of Homeland Security asked Borg to look into what might happen if the internet went down. Borg and his colleagues analysed the economic effects of computer and internet outages in the US from 2000 onwards. Looking at quarterly financial reports from the 20 companies that claimed to be most affected in each case, as well as more general economic statistics, they discovered that the financial impact of an outage was surprisingly insignificant – at least for outages that lasted no more than four days, which is all they studied.