Slow performance
Frequent crashes or freezes
Unexpected pop-ups
Programs opening or closing on their own
Browser redirects to unfamiliar sites
New toolbars or extensions you did not install
Unknown files or apps appearing
Antivirus disabled or unable to update
High CPU, memory, or disk usage
Emails or messages sent from your account without you
Security settings changing by themselves
Missing files or corrupted data
Unusual network activity
Login problems on accounts you use
Computer overheating without heavy use