Another user had the same problem and reported it on the Joplin Discord Channel Discord
STEPS TAKEN:
Updated my Windows 10 Security.
Downloaded the file with Firefox.
Scanned the file in my downloads folder, no threats found.
Installed Opera.
Downloaded the file with Opera.
Download interrupted with message: "Interrupted: Virus detected".
Windows 10 Security blocked and quarantined the file.
Uninstalled Opera.
Downloaded the file with Firefox.
Windows 10 Security blocked and quarantined the file.
Downloaded the file with Google Chrome.
Windows 10 Security blocked and quarantined the file.
The only strange thing is that the first time I downloaded the file, using Firefox, Windows 10 Security didn't find any viruses. It started finding the virus after installing Opera and downloading it with Opera. I'm not sure what to make of this, maybe Opera changed something on the computer.
I have turned off Real-time protection, downloaded the file and uploaded it to the VirusTotal website to be scanned. The result said that 0 out of 60 Security Vendors flagged the file as malicious.
After that I turned back on Real-time protection, scanned the file and Windows Defender gave again the alarm. I guess it's a false positive.
I have the same problem,today with the file saved on download folder.
I aldeady installed Joplin 2.5.10 some days ago and windows defender did not detect any virus.
So I ran Update-MpSignature but Defender is still killing the download (I don't actually need it for an install or anything, just trying to help to see what the issue might be).
I have updated the signature to 464 and again it didn't give me the alert.
It gave me the alert with 449, but only with the second and subsequent scans, and it didn't give me the alert with 458 and 464. But Daeraxa had the problem with 458.
I haven't found out yet how to report the problem to Microsoft, but I don't have the problem anymore so I will just try to find out how to report it for the next time it happens and leave it at that.
For the people that still have the problem, I guess the problem will solve itself in the next hours, days, after some other signature updates
I have again installed the Opera browser and Microsoft Defender started alerting again, so I decided to send the file Joplin-Setup-2.5.10.exe for analysis.
In the Virus & Threat protection settings there is a link to submit a sample manually.