Members of the 11th Reconnaissance Squadron from Indian Springs, Nevada, perform pre-flight checks on the Predator unmanned aerial vehicle prior to a mission, at an undisclosed location in this November 9, 2001 file photograph. [Photo/Agencies]

* Officials still investigating source of virus

* Infection said resisting efforts to remove it

WASHINGTON - The US government's unmanned Predator and Reaper drones are continuing to fly remote missions overseas despite a computer virus that has infected the plane's US-based cockpits, according to one source familiar with the infection.

Government officials are still investigating whether the virus is benign, and how it managed to infect the heavily protected computer systems at Creech Air Force Base in Nevada, where US pilots remotely fly the planes on their missions over Iraq, Afghanistan and elsewhere.

"Something is going on, but it has not had any impact on the missions overseas," said the source, who was not authorized to speak publicly.

Armed tactical unmanned planes have become an increasingly valuable tool used by the US government to track and attack individuals and small groups overseas, but the virus underscores the vulnerability of such systems to attacks on the computer networks used to fly them from great distances.

Wired magazine first reported the virus infection on its website on Friday and said it was logging pilots' every keystroke as they remotely flew missions over Afghanistan and elsewhere.

Wired said the problem was first detected nearly two weeks ago by the US military's Host-Based Security System, but there were no confirmed incidents of classified information being lost or sent to an outside source.

The virus had resisted multiple efforts to remove it from Creech's computers, Wired said, quoting network security specialists.

The US military and intelligence communities have used Predator and Reaper drones, built by privately held General Atomics in San Diego, to carry out increasingly precise attacks on top Al Qaeda officials and other US targets in Pakistan, Afghanistan and Yemen.

Last week, US officials confirmed that Anwar al-Awlaki, an American-born cleric linked to Al Qaeda, was killed in a CIA drone strike in Yemen.

In August, al Qaeda's second-in-command, Atiyah abd al-Rahman was killed in a drone strike in northwest Pakistan. Ilyas Kashmiri, an alleged leader of both al Qaeda and one of its Pakistan-based affiliates, was killed in a suspected US drone strike in June.

The US military has achieved its goal of flying 60 combat air patrols overseas with the unmanned planes, according to one US defense official.

The CIA now operates Predator and Reaper unmanned aircraft over at least five countries including Yemen, Afghanistan and Libya.