1. A short battery life or excessive battery usage
There could be a process going in the background while the screen is off if your phone gets heated for no apparent reason, even while it's not charging. Check your phone battery use to see if there are any indications of malware on your device.
Goto Settings > Battery > Battery Usage
Look for an unknown app and uninstall it.
2. Look for unexpected app installations
If you find random apps loaded on your phone, that's another indication of malware or phone hacking. These are apps that you did not install yourself.
Goto Settings > Apps
If you find an unknown app, uninstall it immediately.
3. Unusual High Data Usage Rate
Someone with a virus could be transmitting your confidential information back to a third party via an app that is continually operating and talking with malicious actors.
Goto Settings > Wireless & networks > Data Usage
Check every app usage & uninstall anything that appears suspicious.
4. Pop-Ups and Ads
All types of websites use pop-ups, which come in a variety of sizes, shapes, and time frames. Do not click on them.
5. Applications and the phone keep crashing
Viruses are sometimes to blame for these issues.
• Open Google Play Store.
• Click on the profile icon on the right side.
• Click on Play Protect.
• Tap Scan to begin scanning your phone and applications.
As an alternative (Malwarebytes), this is one of the best apps to check if your phone has been hacked.