About six weeks ago, users of Facebook's Android application noticed that they were being asked to install a new version—without going to the Google Play app store.

Android is far more permissive than iOS regarding the installation of third-party applications, even allowing installation from third-party sources if the user explicitly allows it. However, it's unusual for applications delivered through the official Google store to receive updates outside of the store's updating mechanism.

Google has now changed the Google Play store polices in an apparent attempt to avoid Facebook-like end runs around store-delivered updates. Under the "Dangerous Products" section of the Google Play developer policies, Google now states that "[a]n app downloaded from Google Play may not modify, replace or update its own APK binary code using any method other than Google Play's update mechanism." A Droid-Life article says the language update occurred Thursday. APK (standing for application package file) is the file format used to install applications on Android.

The app store policy already banned "applications that cause users to unknowingly download or install applications from sources outside of Google Play," but did not explicitly address updates until yesterday.

There are certainly legitimate reasons to ban such a practice—it's easy to imagine the creator of a malicious application enticing users with a seemingly legit app and then updating it with malware. No one expects Facebook to do that, but the change in Google's legalese could force the company to stop updating its app outside the Google Play store.

We've asked Google if this is a completely new policy or merely a more explicit statement of a preexisting policy. We also asked how it will be enforced and whether developers who violate the policy will be forced to submit new versions of their application. We contacted Facebook to ask if it believes its Android app violates the policy and, if so, whether Facebook will remove the auto-updating functionality. (This would be the regular Facebook app, not the new Facebook Home.) We'll provide an update if we get any new information.

Google does in some cases remove applications from Google Play when they violate store policies, but may provide a warning to the developer before doing so. Facebook could thus avoid having its app pulled off the store if it changes how it works in a timely manner.