I've accepted for a while now that it's impossible to silently install an application on Android - that is, to have a program install an application bundled as an APK without providing the standard OS installation prompt and going through the app installer activity. But now I've picked up a copy of the Appbrain fast web installer, and it does exactly this.
How on earth is this possible? :D
IF you can work out what the standard installer does when it installs, you can replicate that behaviour in your app, however yours would need quite extensive permissions to do everything properly.
Seriously, don't even try.
You can ( in a very hackish way ) install apps silently using adb. You have to enable USB Debugging, but just push the APK to /data/app. ie:
adb push MyApp.apk /data/app
adb install MyApp.apk (cleaner way)
The second command MAY prompt for an installation, I don't remember off the top of my head.
I think the clue is pretty much in this statement I found here in the FAQ.
The fast web install worked for me yesterday, but it doesn't work anymore today. What's wrong?
The permission to install apps directly on your phone needs to be refreshed once every few days. Go back to the "Fast Web Install" app on your phone and click the button to give us the permission again. We are working on a future update that will optionally automatically refresh this setting.
I presume this is very similar to what Google does in the kill switch. I am assuming that the kill switch is an application on my device, just hidden from me. When Google wants to remove an application, it silently uninstalls it without asking for our permission. I am very sure this security hole is of their making. Now we just need to figure that out... =D