Modern malware often operates subtly, avoiding detection while stealing data. Signs of infection include sudden slowdowns, frequent freezes, or unknown processes. Start with Microsoft Defender, built into Windows 11 via the Windows Security suite. Open it from the Start menu; green checkmarks indicate safety, while yellow or red icons signal issues. Check Virus & threat protection for recent scans and Protection history for actions taken. Run a Full scan for a deeper check, or use the Microsoft Defender Antivirus (offline scan) to restart into the Windows Recovery Environment and detect cloaked threats. Ensure the firewall is active for all network types under Firewall & network protection.

For a second opinion, use Malwarebytes free on-demand scanner. It offers Quick, Custom, and Deep scans, with options to quarantine or delete threats. Malwarebytes AdwCleaner targets adware and junk other tools miss. Paid Malwarebytes tiers add real-time protection and browser scam blocking, though not essential if you practice safe habits. Using multiple scanners sequentially — not simultaneously — provides comprehensive coverage without conflicts.