Back in 2015, about a year after Russia annexed Crimea, Russian hackers wrested control of Ukraine's power grid and cut off electricity at three different companies.
Some 30 substations were switched off, and about 230,000 people were left without electricity for up to six hours.
They didn't have lights or, in many cases, heat.
Being left without heat in the dead of winter isn't just an inconvenience, it's a safety hazard.
And it's one we might all have to deal with pretty soon.
Because as fall passes and we trek further into winter's frosty belly, we're looking at a potential cataclysm of energy supply disruption - a roiling blizzard of sanctions, cyberattacks, and even sabotage that could leave us all in the cold.
It begins on December 5.
That's the deadline Western powers set to impose an energy import ban on Russian oil and gas.
Of course, some countries are more reliant on Russia for energy than others, and a collective rush to find supplies elsewhere could lead to a global energy price spike.
So the idea of banning oil and gas imports was quickly watered down to a price cap.
Thus, this week, the European Commission, the EU's executive body, asked its 27 member states to approve a price cap of $60 per barrel.
That's well below the Brent crude price (the international benchmark), which is currently $88 a barrel.
It also coincides with the implementation of a separate EU embargo on Russian oil shipments, as well as a similar cap on import prices for natural gas.
Of course, the balancing act between damaging Russia's energy sector while continuing to patronize it will be difficult, if not impossible.
Russia itself certainly isn't keen to cooperate, either.
Amid the price cap negotiations, Russia said it doesn't plan to supply oil or gas to any countries supporting a price cap.
And why should it?
The country has already cut its gas supplies to Europe by 88% over the past year, causing the wholesale price of gas to increase by 210% over the same period.