 
During the Soviet occupation the CIA armed the mujahideen. They had a rule that no weapon in Afghanistan could be traced back to the west, so they supplied Soviet designed equipment from Egypt and China. In the mid-eighties the Soviets threatened to shut down the insurgency with aggressive and highly trained spetnaz commandos and the Hind helicopter.
The CIA responded by arming the mujahideen with the SA-7, a shoulder fired surface-to-air-missile built by the Soviets and once used by the Vietcong. An imitation of the American Redeye, The SA-7 was a heat-seeker small enough to be carried on mule-back. Unfortunately the Soviet technology was inferior and the supply limited. The SA-7 didn't cut it.
The British-built Blowpipe followed. Sold on the open market, it was possible to claim it was not CIA supplied. But the blowpipe relied on line of sight guidance. Only a well trained operator could connect a truck-sized airship and a tiny missile in the absolutely huge sky. After the Falklands the British had to admit even well trained operators couldn't score hits reliably. Strike two.
One option remained, the American Stinger. The Stinger was an upgrade of the user-friendly and reliable Redeye. The Redeye searched the sky for something hot, slid up behind it faster than sound, thrust itself in the exhaust-pipe and pow! The Stinger upgrade was twice as fast and could hit targets face-on; a nice quality since one might be dead before seeing the back of a Hind. But as the Stinger was not sold on the market, any found on mujahideen had to have come from the United States. The CIA decided to risk an open war with the Soviets by arming the mujahideen with the Stinger. After a few were shot down, the Hinds took to flying higher and faster, losing much of their punch.
When the war ended the CIA panicked a little. They needed the unused Stingers back before one downed a commercial jet in a terror attack. The CIA bought Stingers back for $150,000 each, accounting for most of them. There were fears in 2001 that the Taliban still had a few left, and that we might lose aircraft to our own weapons. Osama is supposed to have Stingers posted in his convoy, although I suspect they are all bought back or used up by now.