Sudden battery drain
Phone overheating when idle
Unusually slow performance
Frequent app crashes
Pop-up ads appearing outside your browser
Apps you did not install
Unexplained data usage spikes
Settings changing by themselves
Browser homepage or search engine changing
Unknown charges or texts sent from your phone
Apps requesting unusual permissions
Phone restarting or freezing often
Security alerts from your device or carrier
Strange files, icons, or notifications appearing
Contacts receiving messages you did not send