I recently turned on the app locking feature in ZDBox just to test it out and see how useful it was. It worked flawlessly in terms of locking the apps, I selected an app and it asked me for a password.
The problem is that there are so many workarounds to apps that lock individual apps. I only did this with ZDBox but I'm certain it applies to all other app lockers as well.
I assume most people, especially the average user, would simply assume that as soon as it's turned on that all their apps they locked are safe. This is false. Here are the workarounds I found. And I'll also post what I believe would fix the vulnerability.
1. Use a 3rd party task killer (I used SystemPanel)to simply "end tasK" on the app locker. This deactivates the app locker and gives you full access to every app on the phone.
2. Use the built in task killer to end the app. Similar to the one I mentioned above.
3. Access the Android Market to download a task killer
4. This would only work if installing apps from unknown sources was check marked. I could just download any apk off the web and install a task killer yet again.
I think only after you've locked all of those vulnerabilities, that an app locker would actually work. That's assuming I've covered all the vulnerabilities.
But at that point, why bother with the app locker when the default lockscreen will work just fine and has far less (if any) vulnerabilities?