See also
When you run a standard antivirus from within Windows, it relies on the operating system’s API (Application Programming Interface). If a rootkit has hooked into the kernel, it can simply “lie” to the antivirus, hiding its files, processes, and registry keys. The scanner sees a clean system; the malware continues to operate.
If your computer shows “Bootmgr is missing” or “Operating system not found” after malware removal: avg rescue iso
