We found some forgotten variola (smallpox) at the FDA laboratories in Bethesda, Maryland! They were fully sealed and there's no evidence of tampering, and are now located at the secure BSL-4 CDC laboratory in Atlanta, Georgia, where the rest of the US stockpile is located.
The last naturally-occurring Variola major case was in a Bangladeshi girl in 1975, and the last Variola minor case was in a hospital cook in Somalia, in 1977. Eradication was complete by early 1978, and was formally declared in 1980.
In late 1978, a medical photographer became infected by a smallpox sample kept at the University of Birmingham, and subsequently died from the disease. One other person also became infected, but survived. The researcher who was overseeing the photography operation was distraught and committed suicide soon after the photographer's death. After this, the WHO strongly encouraged all countries to destroy their stockpiles of smallpox.
There was significant resistance to the recommendation and pressure by both Russia and the United States, and today there are two formally declared laboratories that have the live virus - the CDC in Atlanta, Georgia, and VECTOR in Koltsovo, Russia.
Having worked in several labs, there's this fear of throwing things out that people might one day come back and need, or want to use again. Even samples that we can hardly identify, waaaaay back in the -80C freezers, get kept around unless we know what they are and who was using them and that they wish to destroy the sample or declare it unsuitable for future research. Stuff gets shoved to the back, and you don't look at it for years or sometimes decades. There are some truly bizarre things to be found when cleaning old freezers...but hopefully I never come across something like this.
There are probably more smallpox samples out there, in former Soviet states, and in the US. Hopefully they're all as well-sealed and safe as this one was.