A new Android update is rolling out that will add a bit more security when it comes to apps that may harm your device. The update from Google intends to make sure that apps installed on your device — from Google Play or elsewhere — are playing nice and "behaving in a safe manner". Currently the system scans applications at the time you install them, but now it will continuously check all the apps on your device, even after they've been installed.
With the update, users with potentially harmful apps will see an alert on their device, at which time they can take proper action. While bad apps & installs are rare, those who download apps from third-party sources outside of Google Play may see them more often. By continuously checking the apps after they've been installed, Google can now look for new malware code that may already be on your device as well.
Google notes that the new update won't necessarily keep users from installing bogus apps though, such as fake virus scanners or the $3.99 Virus Shield which did nothing to protect users whatsoever.
Source: [Official Android Blog]http://officialandroid.blogspot.com/2014/04/expanding-googles-security-services-for.html)