A while back, DIA posted this piece titled This Week in DIA History: DIA Identifies Leak of Classified KH-11 Capabilities.
Here’s an excerpt:
In 1978, analysts noted a sizeable increase in Soviet efforts to avoid satellite detection of their activities — even of weapon systems previously photographed. Although the Soviets knew the KH-11 satellite passed over the USSR, they had misclassified it as a non-photographic satellite. Suddenly, KH-11 collection on troop and equipment deployments, SS-20 mobile missiles and Backfire Bombers diminished. This provided clear indication that the Soviets obtained new, damaging information on the true capabilities of the KH-11.