Even turning off your iPhone may not keep it safe from hackers. But experts say most people don’t have much to worry about.

Researchers at the Technical University of Darmstadt in Germany have discovered that iPhones can be vulnerable to security threats even when they are turned off. Wireless chips, including Bluetooth, operate in low-power mode when the power is turned off. Malicious actors can abuse the low-power mode to deploy malware.

“When a user turns off their device through the phone’s menu or power button, they have a reasonable suspicion that all processors are turned off, but that’s not the case,” Eugene Kolodenker, a senior security intelligence engineer at cybersecurity firm Lookout who was not involved in the German investigation, told Lifewire in an email interview. “Services like FindMy need to work even when devices are turned off. This requires a processor that keeps running.”

The German researchers investigated the iPhone's low power mode (LPM), which supports near-field communication, ultra-wideband and Bluetooth.