Sudden slow performance
Frequent crashes or freezes
Unexpected pop-ups or ads
Programs opening or closing by themselves
Unknown apps or files appearing
Browser homepage or search engine changing
New toolbars or extensions you did not install
Antivirus or security settings being disabled
Unusual network activity or high data usage
Emails or messages sent from your account without your action
Computer fans running loudly when idle
Files missing, renamed, or encrypted
Frequent error messages
Unable to access certain websites
Random redirects in your browser
Security alerts from antivirus or Windows Defender
Strange login activity on your accounts
USB drives or external devices behaving oddly