The default Windows Security application that comes with Windows 11/10 OS provides basic protection for PCs, including Windows Defender Antivirus and Firewall. However, some users have reported that after a malware attack, the Windows Security Service is missing. This guide provides methods to fix this issue. The Windows Security Service is required by Windows Security to handle device protection and health information. If the malware has disabled or corrupted it, you can try running a malware scan using a 3rd-party antivirus, manually starting the service in the Services Manager, running SFC or DISM scans, resetting Windows Security, or repairing/reinstalling Windows. Running a good antivirus program at boot time or in Safe Mode can help recover Windows from malware, and Windows Security can remove malware, but more complicated cases may require Bootable System Rescue Disks.