Security researchers said they uncovered a vulnerability that could have allowed hackers to commandeer millions of Android devices equipped with mobile chipsets made by Qualcomm and MediaTek.

The vulnerability resided in ALAC—short for Apple Lossless Audio Codec and also known as Apple Lossless—which is an audio format introduced by Apple in 2004 to deliver lossless audio over the Internet. While Apple has updated its proprietary version of the decoder to fix security vulnerabilities over the years, an open-source version used by Qualcomm and MediaTek had not been updated since 2011.