It was called Operation: INFEKTION, and it was a campaign to spread false information that the United States invented HIV/AIDS and dispersed it throughout various populations.
The Soviets did this in an attempt to undermine the credibility of the Americans abroad and instill sympathies for themselves among native populations. This campaign was surprisingly successful. Many native populations believed American military bases were a major cause of the outbreak of the disease and were already wary of foreigners.
Historians believe the Soviets were also attempting to distract foreign powers from their own offensive biological warfare program. It is believed that the Soviet Union used variations of anthrax, tularemia, the plague, and cholera!