In the last few years, intelligence analysts have noted that very few portable anti-aircraft missiles have been discovered in any of the thousands of Taliban and al Qaeda weapons caches found in Afghanistan. It is generally believed, at least by the mass media, that there are thousands of these portable missiles, particularly the Russian SAM-7 (and some later versions) on the black market. Maybe, but not really. Part of the reason is that it is easy to track a missile, used in a successful attack on military or commercial aircraft, to the country (or even factory) or origin. For that reason, few of these missiles apparently make it into the black market, and many of those that are there, are too old to be useful. The manufacturers do not want to take the heat for a crashed airliner. It's bad for business.
While the SAM-7 is still made, many of those available to terrorists are old and basically useless. Some later model Russian missiles have been recovered in anti-terrorist raids in Iraq, and some of these also had become inoperative due to age or poor handling. There are still some American Stinger missiles from the 1980s Afghan war out there, but their batteries have long since died, rendering the missiles useless. Russian made missiles suffer from the same problems, and all these missiles have other components, like the rocket motor, that do not age well.
These missiles were used in Iraq, without much success. Early in the war, up to a dozen Russian made missiles have been fired in Iraq a year. Few aircraft were hit, and most were able to land. It's uncertain exactly how many missiles were fired because several are known to have been duds (because of missile parts found), and other duds have probably not been found. So the missiles are still a threat, but not a large threat, at least judging by the damage these missiles have actually done in the last two decades. There were lots of viable SAM-7s in Iraq because Saddam had bought new ones, and tried to keep older models in good shape.
While there have been so few incidents of portable surface to air missiles (SAMs) use in Afghanistan, the danger remains. As a result of that danger, the U.S. Air Force has all its C-17s and C-130s equipped with missile detection and countermeasures systems. A few of these countermeasures use lasers or infrared light, which blind the heat seeker on the missile. Most countermeasures, however, use flares, which draw the missile away from the aircraft using their high heat. The most modern missiles are not fooled by the flares, which is why the more expensive laser and infrared based systems are preferred. These defensive systems cost between one and four million dollars per aircraft, and weigh between 300-500 pounds.
No one is sure exactly how many commercial aircraft have been brought down by these missiles. Between 1975 (when the missiles first began to show up on the black market) and 1992 (the last known incident of an aircraft being downed), between 29 and 40 commercial aircraft were shot down. Between 550 and 700 people were killed. The uncertainty arises from the fact that nearly all these aircraft were lost in Africa, or other out of the way places where the exact cause of an aircraft crashing could not be confirmed. All the aircraft were smaller, two or three engine commercial types, usually quite old. But the missiles are a danger, just not nearly as large a threat as the headlines imply.