A built-in Windows10 Antivirus can be use to download viruses
The discovery was made by Mohammad Askar (via Bleeping Computer), a security penetration tester and instructor who has posted hundreds of security articles, according to his Udemy profile."Well, you can download a file from the internet using Windows Defender itself. In this example, I was able to download Cobalt Strike beacon using the binary 'MpCmdRun.exe' which is the 'Microsoft Malware Protection Command Line'," Askar stated on Twitter.
This effectively allows a local attacker to leverage Defender as what is called a living-off-the-land binary (LOLBin). That's when legitimate software is used for something malicious—in this case, using an antivirus program to download a virus.