A major aspect supporting Team B's "window of vulnerability" sentiment was confirmed when Sergei Popov defected. His testimony led to the discovery in the 1990s that General Secretary Mikhail Gorbachev and his predecessors had clandestinely overseen the development of ever-stronger nuclear weapons. They also actively spread disinformation about the nature of the "Biopreparat" program. This program breached the 1972 Biological Weapons Convention (BWC) that was to eliminate all biological weapons. Instead, the Soviet Union had engineered, produced, and stockpiled tons of biological agents after signing the 1972 BWC, rationalizing this deceit to the 30,000 or so Soviet biologists, by claiming that the US was doing the same. Popov and others later denounced their Soviet superiors for creating this asymmetry of vulnerability and for misleading them.