Originally Posted by spikexp
Well, APK have no DRM or no security at the base. Some app might require too register, but I only found one of those in all the app I've tried (and I was able to find a better free alternative).
That's not 100% accurate. The developer of a paid app can use the licensing model for the app. In that case the app is linked to your account and periodically contacts a server to verify it is legitimate. If you were to copy that app to a different device it would fail with a license error when launched.