Security researchers discovered a new way to hack the Mac’s built-in webcam this week, and the method is undetectable by users.

Apple built a green LED light into every Mac with firmware-level protection that turns on anytime the sensor is tripped by unauthorized access. The security feature has become increasingly difficult for hackers to beat, but former NSA staffer Patrick Wardle found a way to piggyback on outgoing feeds and record them.

Wardle, who now leads cyber R&D for security intelligence firm Synack, created an OS X malware sample showing how hackers could stealthily monitor your Mac so that anytime you initiate a video session, the malware covertly records the audio and video.

This hack would work on any video or video chat apps, such as Skype and FaceTime, potentially exposing intimate details of the user’s life. Cult of Mac reached out to Apple for comment on the potential threat, but did not receive a reply.

Preventive measures for Mac hack

To combat the potential Mac hack, Wardle created a tool called OverSight. The free app monitors your webcam and microphone activities, then notifies you if a malicious secondary app accesses the feed. You can then choose to allow or block access.

But if you want to be absolutely certain no one is looking through your webcam, take the Mark Zuckerberg route and put tape over the lens.