ES File Explorer is a popular file explorer app for Android. Even though it is proprietary, I must admit, that I came in touch with it too some years ago.
As Techcrunch reports, a security researcher now detected a backdoor in the app, which allows users on the same local area network as the victim to access the contents of the phone.
This example shows, how important it is to have free software, which can be audited by everyone.
Just a quick hint: Mike Kuketz released a blog post about how you can use Blokada to block ads and trackers on your android device. In his post, he explains how Blokada uses a private VPN to block DNS requests to known tracker/ad sites and recommends a set of rules to configure the app for best experience.
He also briefly mentions F-Droid and gives some arguments, why you should get your apps from there instead of the Play Store.
The blog post is written in German and is available on kuketz-blog.de.