Last Updated: October 2017
In Windows 10 Fall Creators Update, the active Antivirus product can dynamically scan Office documents via the Antivirus API for Office when you open them. This helps the active Antivirus product to detect malicious documents that obfuscate malicious content by employing techniques like document encryption. This scanning occurs with all versions of Office documents and could result in a delay of up to 1 second per document.
Microsoft is investigating this issue and will post an update here once the issue is resolved. For more information on this behavior, see Introduction to the Antivirus API Reference for Office.
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