An upcoming update to Google Play Services will allow it to scan your apps after installation for malware, with a new Verify Apps feature.
Verify Apps scans any apps not installed via Google Play, and informs you if they are dangerous or contain threats. The scan currently happens only at installation, but soon it will continue to scan your apps afterwards. This means if a new threat is uncovered after you install an app, Android will be able to notify you.
The new version of Verify Apps will therefore run constantly in the background, instead of just activating when apps are side loaded (installed from outside Google Play). This further extends Android’s security, and makes side-loading safer than it is today. Most Android malware comes packaged with side-loaded apps from unofficial stores, so this is a good way to combat the problem.