You have a Microsoft 365 subscription that uses Microsoft Defender for Office 365.

Safe Attachments for SharePoint, OneDrive, and Microsoft Teams

In organizations with Microsoft Defender for Office 365, Safe Attachments for SharePoint, OneDrive, and Microsoft Teams provides an additional layer of protection against malware. After files are asynchronously scanned by the common virus detection engine in Microsoft 365, Safe Attachments opens files in a virtual environment to see what happens (a process known as detonation). Safe Attachments for SharePoint, OneDrive, and Microsoft Teams also helps detect and block existing files that are identified as malicious in team sites and document libraries.