Hi @JSS CGY ,
Are there any Exchange functions that are not working properly?
According to my research on "Backdoor:MSIL/Chopper.F!dha ", I found that this is a security issue about Windows server, not specific to Exchange. I can provide limited help. So I help you add a "Windows-server-security" tag, which will bring in professional engineers to help you.
Based on my research on this issue, I recommend that you upgrade your Windows server to the latest version and install the relevant Security update. Then you could scan your PC by using Microsoft Defender. In addition, if all the methods cannot be solved, reinstalling the Windows system will be our last choice.
For more information you could refer to: Troubleshoot problems with detecting and removing malware
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