A computer virus was detected in the U.S. drone remote control system, the Wired.com news portal said.
The virus "has infected the cockpits of America's Predator and Reaper drones, logging pilots' every keystroke as they remotely fly missions over Afghanistan and other warzones," it said.
It was first detected two weeks ago but has done no damage to U.S. military operations so far. There has been no confirmation so far that the virus sent classified information to an outside source.
"We keep wiping it off, and it keeps coming back... We think it's benign. But we just don't know," the portal quoted a source familiar with the situation as saying.
It is still unclear whether the virus attack was deliberate or accidental.
"It may be a common piece of malware that just happened to make its way into these sensitive networks," the website said.
The Air Force declined to comment directly on the virus.
"We generally do not discuss specific vulnerabilities, threats, or responses to our computer networks, since that helps people looking to exploit or attack our systems to refine their approach," said Lt. Col. Tadd Sholtis, a spokesman for Air Combat Command, which oversees the drones and all other Air Force tactical aircraft.
Drone systems have been widely used by the U.S. military in Afghanistan and northwestern Pakistan. According to the Pakistani media, the overall number of U.S. drone missions in the region has been steadily increasing.
The issue of drone U.S. has become an irritant in U.S.-Pakistani relations recently. Pakistani media estimates that at least 115 drone attacks were recorded in the country's northwest last year, in which at least 670 people were killed. In 2009 about 420 people were killed in 45 airstrikes.
