From AVAST:
Web Shield component detections when accessing Microsoft Office
New incident: Monitoring
Users may experience a detection from our Web Shield component when accessing Microsoft Office, this is due to an expired certificate on Microsoft’s end. It is possible to temporarily add an exclusion for office.net to the exclusions, however, as the issue is the expired certificate itself, the web browser will then likely further block access. Once Microsoft applies a new valid certificate, the issue will be resolved
