Insurgents obtained information from U.S. Predator drones flying over Iraq using off-the-shelf software, Adm. Mike Mullen confirmed. ((Reuters))

Recent interception of video feeds from U.S. drone aircraft caused no significant damage, the country's top military officer said Friday.

Hackers obtained information from drones flying over Iraq, Adm. Mike Mullen confirmed Friday, a day after the Wall Street Journal broke the news.

The drones serve as the military's eyes in the sky for surveillance and intelligence gathering. Mullen said he was very concerned about the issue and cyber security in general.

WSJ reported Thursday that Shia fighters in Iraq used off-the-shelf software called SkyGrabber to intercept live video feeds from U.S. Predator drones, potentially providing them with critical data about what the U.S. military may be targeting, including buildings, roads and other facilities.

The interception, first done at least a year ago, was possible because the remotely flown planes had unprotected communications links.

Within the last several months, the military has found evidence of at least one instance where insurgents in Afghanistan also monitored U.S. drone video, a defence official told The Associated Press. He had no details on how many times it was done in Afghanistan or by which group.

The Defence Department has addressed the issue, and is working to encrypt all of its drone video feeds from Iraq, Afghanistan and Pakistan, defence officials said. One defence official noted that upgrading the encryption in the drones is a lengthy process because there are at least 600 unmanned vehicles along with thousands of ground stations to address.

Officials said that systems in key threat areas were upgraded first.