Description:
Under Windows 7 X64, when using Windows Update to Update the system, the relevant Update defined by Windows Defender malware could not be installed, and 8050800C error was always returned. At this point, when Windows Defender updates the definition, he will also report that the definition cannot be updated.
Solutions:
The following solution source: https://social.technet.microsoft.com/Forums/en-US/7b44be83-8a2e-4e3e-a851-cbc3076e4817/error-8050800c?forum=w7itprosecurity
1. Save the following as a batch file and run it in administrator mode:

@echo off

net stop bits
net stop wuauserv
net stop appidsvc
net stop cryptsvc

Del "%ALLUSERSPROFILE%\Application Data\Microsoft\Network\Downloader\qmgr*.dat"
Ren %systemroot%\SoftwareDistribution SoftwareDistribution.bak
Ren %systemroot%\system32\catroot2 catroot2.bak
sc.exe sdset bits D:(A;;CCLCSWRPWPDTLOCRRC;;;SY)(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;BA)(A;;CCLCSWLOCRRC;;;AU)(A;;CCLCSWRPWPDTLOCRRC;;;PU)
sc.exe sdset wuauserv D:(A;;CCLCSWRPWPDTLOCRRC;;;SY)(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;BA)(A;;CCLCSWLOCRRC;;;AU)(A;;CCLCSWRPWPDTLOCRRC;;;PU)
cd /d %windir%\system32
regsvr32.exe atl.dll /s
regsvr32.exe urlmon.dll /s
regsvr32.exe mshtml.dll /s
regsvr32.exe shdocvw.dll /s
regsvr32.exe browseui.dll /s
regsvr32.exe jscript.dll /s
regsvr32.exe vbscript.dll /s
regsvr32.exe scrrun.dll /s
regsvr32.exe msxml.dll /s
regsvr32.exe msxml3.dll /s
regsvr32.exe msxml6.dll /s
regsvr32.exe actxprxy.dll /s
regsvr32.exe softpub.dll /s
regsvr32.exe wintrust.dll /s
regsvr32.exe dssenh.dll /s
regsvr32.exe rsaenh.dll /s
regsvr32.exe gpkcsp.dll /s
regsvr32.exe sccbase.dll /s
regsvr32.exe slbcsp.dll /s
regsvr32.exe cryptdlg.dll /s
regsvr32.exe oleaut32.dll /s
regsvr32.exe ole32.dll /s
regsvr32.exe shell32.dll /s
regsvr32.exe initpki.dll /s
regsvr32.exe wuapi.dll /s
regsvr32.exe wuaueng.dll /s
regsvr32.exe wuaueng1.dll /s
regsvr32.exe wucltui.dll /s
regsvr32.exe wups.dll /s
regsvr32.exe wups2.dll /s
regsvr32.exe wuweb.dll /s
regsvr32.exe qmgr.dll /s
regsvr32.exe qmgrprxy.dll /s
regsvr32.exe wucltux.dll /s
regsvr32.exe muweb.dll /s
regsvr32.exe wuwebv.dll /s


netsh winsock reset

netsh winhttp reset proxy

net start bits
net start wuauserv
net start appidsvc
net start cryptsvc



wuauclt /Updatenow

2. Manually download from here the latest definition library for the corresponding native system version of Windows Defender to install. Note: it is normal for downloaded files to run without any prompt.
3. Manually download the corresponding local system version of KB3177467 patch from here for installation.
4. Manually download the Windows Update troubleshooter from here and run it until it runs out.
5. After running all the above steps, restart the computer.
6. Open Windows Update in the control panel and repeatedly check for updates until no updates are available