When wanting to install the latest version, Windows Defender stopped the execution of the program.

I uploaded the file to Virustotal.com:
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1 of 69 flagged it positively, that is still 1 too many. Please fix whatever malware-like behaviour Voobly might use.

Please read: https://www.voobly.com/forum/thread/333898

It's a false positive. I will try to get in touch with them again and ask them to update their signatures. Thanks for the report.

Please follow the steps below to clear cached detection and obtain the latest malware definitions.

1. Open command prompt as administrator and change directory to c:\Program Files\Windows Defender
2. Run “MpCmdRun.exe -removedefinitions -dynamicsignatures”
3. Run "MpCmdRun.exe -SignatureUpdate"

There should be no detection anymore.

Thanks for the information! Interesting that this arose in January already but I am getting the issue only now, after Voobly failed to update and I tried to do a clean install.

Following these commands sadly did not remove the Windows Defender popup issue. I hope this can be fixed soon.

Could you please show me a screenshot of Windows Defender detecting Voobly client as Malware?

I tried on both Win 10 clients now, and besides the "no digital signature" message, Windows Defender does not seem to care about Voobly Client.