It’s called Pithovirus sibericum and it’s been frozen deep in Siberian permafrost for centuries.
The bug only infects amoebas, but it has scientists worried. Nature reports one researcher calls warming and mining in the area a “recipe for disaster."
Professor Jean-Michel Claverie, from the National Centre of Scientific Research told the BBC, “this is the first time we've seen a virus that's still infectious after this length of time."
Nature says researchers are concerned there may be other, more dangerous viruses sleeping nearly 100 feet deep in the ice.
“If it is true that these viruses survive in the same way those amoeba viruses survive, then smallpox is not eradicated from the planet, only the surface," Claverie began.
"If you start having industrial explorations, people will start to move around the deep permafrost layers.”
That means further exploration could uncover monsters that would threaten millions of lives.
USA Today points out scientists hope other viruses aren’t as tough as the Siberian giant, but they don’t want to take the chance.