Smallpox is extremely deadly (30% fatality rate) so only two labs in the world – CDC in Atlanta and one in Russia – hold samples of the virus.

In 1980, the World Health Assembly declared smallpox eradicated.

Yahoo News reported:

The FBI and the Centers for Disease Control and Prevention are investigating "questionable vials" labeled "smallpox" and found in a freezer last night at a Merck facility outside Philadelphia, according to an alert sent to Department of Homeland Security leadership on Tuesday night.

There were reportedly a total of 15 questionable vials, according to the unclassified "For Official Use Only" alert, a copy of which was obtained by Yahoo News. Five of the vials were labeled as "smallpox" and 10 were labeled as "vaccinia." The vials were secured immediately.

The discovery of the vials prompted a lockdown of the facility, which has since been lifted. The FBI and CDC launched investigations, which remain ongoing.