Verify apps checks if there are Potentially Harmful Apps (PHAs) on your device. If a PHA is found, it warns the user and enables them to uninstall the app. Android Security team correlates app install attempts and DOI devices to find apps that harm the device in order to protect our users. The DOI score indicates an app has a statistically significant lower retention rate if the Z-score is much less than -3.7. When a device stops checking up with Verify apps, it is considered Dead or Insecure (DOI)”]
Source: https://security.googleblog.com/2017/01/silence-speaks-louder-than-words-when.html