Hi, @Duchemin, Dominique
Thank you for posting in Microsoft Q&A forum.
Try to check the Event Viewer log, under the "Applications and Services Logs" section. Look for the "Microsoft Antimalware" log.
The logs for the definition updates can be found in the following directory: %ProgramData%\Microsoft\Microsoft Antimalware\Support. This log file contains information about the updates that have been downloaded and installed on the client machines.
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