WASHINGTON -- Militants in Iraq have used $26 off-the-shelf software to intercept live video feeds from U.S. Predator drones, potentially providing them with information they need to evade or monitor U.S. military operations.

Senior defense and intelligence officials said Iranian-backed insurgents intercepted the video feeds by taking advantage of an unprotected communications link in some of the remotely flown planes' systems. Shiite fighters in Iraq used software programs such as SkyGrabber -- available for as little as $25.95 on the Internet -- to regularly capture drone video feeds, according to a person familiar with reports on the matter.

U.S. officials say there is no evidence that militants were able to take control of the drones or otherwise interfere with their flights. Still, the intercepts could give America's enemies battlefield advantages by removing the element of surprise from certain missions and making it easier for insurgents to determine which roads and buildings are under U.S. surveillance.

The drone intercepts mark the emergence of a shadow cyber war within the U.S.-led conflicts overseas. They also point to a potentially serious vulnerability in Washington's growing network of unmanned drones, which have become the American weapon of choice in both Afghanistan and Pakistan.

The Obama administration has come to rely heavily on the unmanned drones because they allow the U.S. to safely monitor and stalk insurgent targets in areas where sending American troops would be either politically untenable or too risky.