If the OS or phone is compromised at it's root (google rootkit, etc.) Then these can't really protect you.
However since all data flies over their network, and so on, there is no privacy to speak of on cellular. This can really rankle those that wish otherwise.
Example https://arstechnica.com/information-technology/2016/11/powerful-backdoorrootkit-found-preinstalled-on-3-million-android-phones/
I guess these Apps can protect against malware, viruses. What if there is spyware built-in the system or hardware?

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