I think it's hard not to be skeptical when it comes to these things @dds. For me personally, I treat every 'certainty' in life as a maximum of 99.9% I'm also aware there has been some debate about the usefulness of AV apps over the years as you have alluded, and thanks for the link as well, that made for interesting reading.
I spoke to the author of this test @SteveDuncombe regarding your comment, and he had some additional info to pass on the mobile anti-virus apps issue that I thought would be of interest:
CHOICE use the specialist external test lab AV-test.org for the mobile software results. This lab is one of the premier test labs worldwide.
It's correct that Android OS apps do run in a sandbox, so theoretically they are safe and don't communicate between or affect each other. However, in reality, malware can still proliferate for several reasons. For detailed coverage I would refer you to the following Android Authority article "How secure is Android?" which covers it in detail.
The following is a quick summary of the issues. This article quotes Google saying “like all security features, the Application Sandbox is not unbreakable." The article then explains how security can be weakened in several ways:
* Rooting - providing root user access to the device (called rooting) increases the security exposure to malicious applications and potential application flaws. This can be user-initiated or it can actually be done by malware without the user's knowledge.
* Giving privileges - “for an app to be malicious it doesn’t need to have access to the deeper levels of the OS. If an unsuspecting user installs a malicious app which sends premium rate SMS messages and the user granted those privileges to the app when it’s installed, then the malware has successfully been installed without breaking any of the security.”
* Compromised apps - “some malware actually comes with root exploits built-in. This means that when the app is installed it actually roots the device (without the user knowing) and by-passes all the system security.”
I'm not trying to convince anyone one way or another though, and I'd be interested more views on the topic.