Sudden battery drain
Phone overheating when not in use
Unusual data usage spikes
Pop-up ads appearing outside the browser
Apps opening, crashing, or installing by themselves
Unknown apps appearing on the phone
Slower performance than usual
Frequent browser redirects
Contacts receiving strange messages from your phone
Settings changing without your permission
High mobile bill without explanation
Security warnings from antivirus or the system
Phone restarting or freezing often
Camera, microphone, or location turning on unexpectedly
Unfamiliar charges on accounts linked to the phone