In 1966 the Mossad convinced an Iraqi pilot to defect and bring a MiG-21 with him to Israel [1] Not a lot was known about the plane by the west back then, and

In 1966 the Mossad convinced an Iraqi pilot to defect and bring a MiG-21 with him to Israel [1] Not a lot was known about the plane by the west back then, and it was crucial for Israel to know how to defete it in battle. Later in 1967, during aerial battles over the Golan Heights, the Israeli Air Force brought down 6 Syrian MiG-21s without losing any of its Dassault Mirage IIIs. I would assume such operations are being conducted today as well and Russian high-tech equipment found its' way to the west. https://en.wikipedia.org/wiki/Operation_Diamond https://en.wikipedia.org/wiki/Operation_Diamond