If your phone is overheating, even when it is lying idle
Malicious apps running in the background can drain your phone battery faster
Malicious apps running in the background can lead to sudden spike in data usage
If your phone has slowed down suddenly without an apparent reason
If you’re receiving weird pop-ups, do not tap such notifications
If you phone gallery has some random photos or video that you didn't capture
Unexpected calls or messages could be signs of a hacked phone