Three key points in his article. First, there is malware for the macOS operating system that can commander the webcam. Second, the green light next to the camera will always turn on when the webcam is in use. Third, malware can get around this by recording webcam data while you’re regularly using your webcam (e.g. Skype or FaceTime).
One of the most insidious actions of malware is abusing the video capabilities of an infected host to record an unknowing user. Macs, of course, are not immune; malware such as OSX/Eleanor, OSX/Crisis, and others, all attempt to spy on OS X users.
Luckily, modern Macs contain a hardware-based LED indicator that can alert users when the camera is in use. And physically covering the built-in camera also provides a low-tech, albeit highly effective solution.
Still, Mac users often legitimately make use of their built-in webcams. For example, a CEO joining in on an important business meeting, a journalist Skyping with a private source, or the everyday Mac user having an intimate FaceTime session with their partner. Unfortunately, malware can covertly record these, all in an essentially undetectable manner.