Re: cannot delete microsoft security client file after uninstalling microsoft securi
Are you positive you aren't trying to remove something that is part of Windows?
Windows Defender is built into every Windows version from Windows 7 forward.
In Windows 8.1 and 10 Windows Defender is actually what was known as MS Security Essentials in Windows 7.
Since I have zero experience with 8.1 and 10, I'll simply state what I know about Windows 7. When another security program is installed, Windows Defender gets disabled.
Is this program interfering with Avast in any way? If not, don't worry about it.