BAGRAM, Afghanistan - American investigators armed with a "box full" of cash have paid thousands of dollars to buy back stolen computer drives — many of which contain sensitive military data, shopkeepers outside the main U.S. military base in Afghanistan said Friday. But dozens are still on sale, including memory sticks with information ranging from U.S. troop resumes to photographs of Air Force One during President Bush's visit last month. The surfacing of the stolen computer devices has sparked an urgent probe to discover how security could have been breached at the heavily guarded Bagram base, which coordinates the fight against Taliban and al-Qaida militants and includes one of the military's main detention facilities for suspected terrorists. U.S. military spokesman Lt. Mike Cody said he could not comment because an investigation was ongoing. Shopkeepers let an Associated Press reporter review about 40 of the drives on a laptop computer Friday. Most were blank or did not work, but three contained data, including a soldier's military discharge certificate, troop resumes and photographs of Air Force One during Bush's visit to Afghanistan last month. One shopkeeper, who spoke on condition of anonymity because of fear of retribution, said soldiers went around the market outside the base Thursday carrying "a box full of afghanis (the Afghan currency), buying all they could find." He said he sold about 50 for $2,000, roughly $40 each. A day earlier, he was selling them for about half that price. "They said they wanted them all and price wasn't important," the shopkeeper said. The troops hadn't returned to the market by Friday afternoon despite dozens of the flash drives still being available. Another shopkeeper, who declined to be identified for the same reason, said the troops promised to return. Included on some memory drives seen by AP earlier this week were the Social Security numbers of hundreds of soldiers, including four generals, and lists of troops who completed nuclear, chemical and biological warfare training. The Los Angeles Times also reported that some drives had classified military secrets, including maps, charts and intelligence reports that appeared to detail how Taliban and al-Qaida leaders have been using southwestern Pakistan as a planning and training base for attacks in Afghanistan. The documents, which seemed to be based on conversations with Afghan informants and official briefings, outlined how the U.S. military came to focus its search for militants on both sides of the Afghan-Pakistani border, according to the newspaper. The Times also said the drives appeared to contain the identities of Afghan sources spying for U.S. Special Forces that operate out of Bagram. The shopkeepers have said they were not interested in the data and were only selling the drives for the value of the hardware. They say the drives were stolen by some of the 2,000 Afghans employed as cleaners, office staff and laborers at Bagram. Though workers are searched coming in and out of the base, the flash drives are the size of a finger and can easily be concealed on a body. The memory sticks seen Friday included photographs of mine clearing vehicles that appeared to have been damaged by explosions. There were several performance reviews of troops, which included their Social Security numbers. One review reprimanded a soldier for misplacing his weapon. U.S. commander Lt. Gen. Karl W. Eikenberry has ordered a review of policies and procedures relating to the accountability of computer hardware and software at Bagram, outside which hundreds of shops have sprung since the Americans took it over in 2001 after ousting the Taliban for harboring al-Qaida leader Osama bin Laden. The leaked data wasn't the first time secret information has been discovered electronically by reporters in Afghanistan. Shortly after U.S.-led troops invaded Afghanistan in late 2001, a journalist for The Wall Street Journal bought a computer in Kabul that had belonged to al-Qaida. It contained memos of the terrorist group's chemical and biological weapons program, justifications for killing civilians and a propaganda video made from footage of people fleeing from the World Trade Center during the Sept. 11 attacks.