In a paper called iSeeYou: Disabling the MacBook Webcam Indicator LED, security researchers Matthew Brocker and Stephen Checkoway explained a method for remotely operating the Isight webcam in Apple's Macbook laptops. Recent stories indicated that the FBI had this capability, but it's the first indication of how the trick is attained (the researchers reprogrammed the embedded controller in the webcam). They supplied the Washington Post with details and proof-of-concept software. The technique was applied to older model Macbooks, but there's no reason to suspect this wouldn't work against recent machines and machines made by other manufacturers.
MacBooks are designed to prevent software running on the MacBook's central processing unit (CPU) from activating its iSight camera without turning on the light. But researchers figured out how to reprogram the chip inside the camera, known as a micro-controller, to defeat this security feature. In a paper called "iSeeYou: Disabling the MacBook Webcam Indicator LED," Brocker and Checkoway describe how to reprogram the iSight camera's micro-controller to allow the camera and light to be activated independently. That allows the camera to be turned on while the light stays off. Their research is under consideration for an upcoming academic security conference.
The researchers also provided us with a copy of their proof-of-concept software. In the video below, we demonstrate how the camera can be activated without triggering the telltale warning light.
Research shows how MacBook Webcams can spy on their users without warning [Ashkan Soltani and Timothy B. Lee]