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Your phone's virtual assistant may be doing some temp work on the side: Two French researchers have discovered a way to activate Siri or Google Now from afar.

There is a catch, however: Headphones must be plugged into a phone's microphone jack.

As reported by Wired, scientists at the French government agency ANSSI found that, by using the headphone cord as an antenna, they could trick the phone into thinking it is receiving audio commands from the owner.

The hacker, therefore, could silently use the radio attack to make calls, send texts, eavesdrop, navigate the browser to a malware site, or send spam and phishing messages via email and social media.

This possibility, according to researchers José Lopes Esteves and Chaouki Kasmi, raise "critical security" concerns.

"The sky is the limit here. Everything you can do through the voice interface you can do remotely and discreetly through electromagnetic waves," Vincent Strubel, director of their research group at ANSSI, told Wired.

Presented first at this summer's Hack in Paris conference, the study didn't make waves until its recent publication by the IEEE (Institute of Electrical and Electronics Engineers).

Using some off-the-shelf gadgets, the researchers were able to tap into phones anywhere from 6.5 feet to more than 16 feet away, depending on the device used.

Don't throw away your cell phone just yet: According to Wired, the hack has some "serious limitations." Many Android devices, for instance, don't have Google Now enabled from the lockscreen; it can also be set to respond only to commands when it recognizes your voice. Cupertino recently added a similar feature to Siri on iOS 9. It's also likely that, unless you're completely oblivious, you'd notice the browser opening on its own or mysterious texts being sent.

Kasmi and Esteves alerted Apple and Google to their discovery and recommended some fixes, like better shielding on headphone cords or software updates, Wired said.

You could, of course, replace Google Now with Cortana on Android.

Apple, Google, and the ANSSI did not immediately respond to PCMag's request for comment.