You've heard about hackers trying to steal credit card numbers and wipe out bank accounts. But there's another group that many cybersecurity experts say especially worry them.

These criminals are targeting critical infrastructure, like power grids — and what makes them dangerous is that some are backed by governments and big money.

"Turning off water, turning off electricity. Those are all realistic attacks now," said Liam O' Murchu a director with cybersecurity company Symantec, the manufacturer of Norton security products.

Symantec is currently tracking more than 100 government backed groups, more than ten times the number from five years ago.

Using a computer to cause a power outage may seem farfetched, but experts believe it's already happened. Most recently, in December, parts of Ukraine's capital city Kiev lost power because of what was believed to be a cyberattack.

And that wasn't the first time. In December 2015, 225,000 customers in Ukraine lost power, likely as the result of malware being placed on the computer network of a power supply company, according to the Department of Homeland Security. The Ukrainian government has blamed Russia for the 2015 attack.