Mollivirus sibericum, which translates to "soft virus from Siberia", is the fourth such 'giant virus' discovered this century. The same team of scientists discovered another of these, Pithovirus sibericum, last year, and Mollivirus sibericum was isolated from the same sample of permafrost.
These prehistoric viruses are called 'giant viruses' because they're visible by light microscopy, with lengths greater than half a micron - a thousandth of a millimetre. As bugs go, they're big.
If the idea that scientists are going to wake this thing up sounds a little disconcerting – and, to be honest, it's not altogether unlike the opening scenes of a plague disaster movie – don't worry. The researchers say they will only revive the virus if they can be certain it's not a threat to animals or humans.