What is the best security app for Android?
If you're talking about OS security, like antiviruses, that concept is irrelevant with Android because it's based on Linux (the kernel), and such a kernel doesn't require any such "protection" because of its robustness - it won't allow any applications to install themselves silently. When you install an app on your device, make sure you see the permissions it asks for - they should be justified.
However, some manufacturers - like Samsung - modify the vanilla Android framework which might result in security loopholes, like the Exynos exploit[1] in the Galaxy S3 via which an application could obtain root privileges in an unrooted device. Unfortunately, most users are unaware of such loopholes because (obviously) manufacturers don't make such news public. This could be a reason why you should consider switching to vanilla based ROMs, like CyanogenMod. Or stick to Nexus devices, if you're worried about warranty.
As for lateral security, which is useful in cases of theft or loss, Lookout is probably the best option.
IMPORTANT NOTE: If the "thief" is someone even half as smart as me, they can still access your device and use it without much trouble, because Android devices have a special mode called fastboot[2] (Download mode on Samsung devices). Booting into this mode just requires you to press a particular button combination while powering up the device, and once booted, you can connect your device to your PC and completely erase everything on it, essentially making the device as good as new. The IMEI number can also be overwritten, and so can the MAC addresses of the network cards, hence completely changing the "identity" of the device.
Note on ADB: Android Debug Bridge allows you to control your phone via your PC. If your Android OS is below 4.2.x your data is potentially at risk too, if you have USB debugging enabled (disabled by default). If you have a rooted device a custom recovery can easily be installed, which when booted into will provide root ADB access - meaning your entire phone is available to whoever's using it.
However, some manufacturers - like Samsung - modify the vanilla Android framework which might result in security loopholes, like the Exynos exploit[1] in the Galaxy S3 via which an application could obtain root privileges in an unrooted device. Unfortunately, most users are unaware of such loopholes because (obviously) manufacturers don't make such news public. This could be a reason why you should consider switching to vanilla based ROMs, like CyanogenMod. Or stick to Nexus devices, if you're worried about warranty.
As for lateral security, which is useful in cases of theft or loss, Lookout is probably the best option.
IMPORTANT NOTE: If the "thief" is someone even half as smart as me, they can still access your device and use it without much trouble, because Android devices have a special mode called fastboot[2] (Download mode on Samsung devices). Booting into this mode just requires you to press a particular button combination while powering up the device, and once booted, you can connect your device to your PC and completely erase everything on it, essentially making the device as good as new. The IMEI number can also be overwritten, and so can the MAC addresses of the network cards, hence completely changing the "identity" of the device.
Note on ADB: Android Debug Bridge allows you to control your phone via your PC. If your Android OS is below 4.2.x your data is potentially at risk too, if you have USB debugging enabled (disabled by default). If you have a rooted device a custom recovery can easily be installed, which when booted into will provide root ADB access - meaning your entire phone is available to whoever's using it.
