Is the Trojan:Win32/BlockMsav.A!reg threat dangerous? In some cases yes, but if you blocked Windows Defender (msmpeng.exe) with GlassWire then it’s most likely a false positive.
To solve the issue, unblock msmpeng.exe as shown below (search for Antimalware and it will appear). If you click the icon next to its name it will show the app name as msmpeng.exe.
We white list Windows Defender to avoid this scenario but it appears Microsoft recently updated the publisher that signs Windows Defender so GlassWire could not recognize the executable.
Our next update will solve the issue by white listing the newly signed Windows Defender msmpeng.exe.
If you are not using GlassWire and you found this page from the web then perhaps Windows Firewall is probably blocking Windows Defender. You should go to Windows Firewall and choose “restore defaults” then reboot and see if the error goes away.
It’s also possible in some cases (especially if you are not running GlassWire) you may legitimately have this malware and you should do as Windows Defender suggests to solve the problem.