Werner, there is no such instruction on Google Play Anti-Theft anymore.
I can see that Avast tries to make Anti-Theft as a stand-alone app. That's a nice step forward as I don't want whole Mobile Security package in order to get the Anti-Theft feature. But there is a little work to make it better.
First time I couldn't find a way of getting root install of Anti-Theft as I installed it directly from Google Play (without Mobile Security). It took me quite some time to figure it out - so for the others - there is a button "Root mode" at the top of Advanced Settings. It redirects you to Google Play for "Anti-Theft (rooted)", here is the link -
https://play.google.com/store/apps/details?id=com.avast.android.antitheft_setup. But more information about this option for users would be feasible.
The BFU approach is:
1. Having the phone rooted, BFU installs Anti-Theft from Google Play (not rooted version). In Advanced Settings, the root options are greyed out.
2. In Help -> Settings, there is many times "If you installed Anti-Theft rooted, ..." but not a single sentence about how to install it rooted.
3. In Help -> Stealth mode I read "If you installed Anti-Theft rooted, it is also easy to remove Anti-Theft. Start up avast! Mobile Security, and go to Settings, ...". Oh, so there is at least a hint. I don't know how to install it rooted but at least I know that for uninstall I need Mobile Security.
4. Help -> F.A.Q. redirects me to avast! Mobile Security FAQ web page. Which I don't have installed in first place. And there is no valuable info for this case anyway.
So what would be nice is:
1. To have in description of Anti-Theft on Google Play link to the rooted version.
2. Update the Help section to mention possibilities of how to get the rooted installation.