Two security researchers demonstrated that the Android Factory Reset process fails to wipe private data from Android mobile devices. Researchers at Cambridge University, Laurent Simon and Ross Anderson, revealed that more than half a billion Android devices could have data recovered due to flaws in the default wiping process. The experts have analyzed Android 21 devices from 5 different vendors, including Samsung, HTC, and Nexus running Android versions 2.3 to 4.3. They are able to retrieve encryption keys and master tokens for Google and Facebook in 80 percent of cases.”]
Source: https://securityaffairs.co/wordpress/37065/hacking/android-factory-reset-flaw.html