Signs that deserve attention
Unexpected browser redirects, security software being disabled, unknown applications, repeated pop-ups, unexplained account logins or sudden system behaviour can indicate compromise. Some performance problems have harmless causes, so avoid assuming every slow computer has a virus.
Contain before you clean
If the device may be compromised, avoid entering banking or important passwords on it. Disconnect unnecessary external drives and consider taking the computer offline while you assess the problem. Use trusted security tools from their official sources.
Change passwords from a trusted device
If accounts may have been exposed, change important passwords from a different known-clean device and enable multi-factor authentication. Review recent sign-ins and recovery information for email, financial and business accounts.