An ancient virus has come back to life after lying dormant for at least 30,000 years, scientists say.
It was found frozen in a deep layer of the Siberian permafrost, but after it thawed it became infectious once again.
The French scientists say the contagion poses no danger to humans or animals, but other viruses could be unleashed as the ground becomes exposed.
The study is published in the Proceedings of the National Academy of Sciences (PNAS).
Professor Jean-Michel Claverie, from the National Centre of Scientific Research (CNRS) at the University of Aix-Marseille in France, said: "This is the first time we've seen a virus that's still infectious after this length of time."