Office 365 scans for the link in the Email bodies for blacklist and suspicious domains, in this case, the link enclosed, is to a SharePoint document.
PhishPoint Attack Flow
Attackers use to send an Email that contains a hyperlink pointed to a SharePoint document and the body of the email contains the fake SharePoint invitation to collaborate.
The page contains “Access Document” with the hyperlink added to the malicious URL, when the user clicks on the link it takes to the spoofed Office 365 login page and when the user attempts to log in the credentials will be harvested by attackers.
As the malicious link embedded inside of the SharePoint document, Office 365 didn’t identify it as the threat. “In order to identify this threat, Microsoft would have to scan links within shared documents for phishing URLs,”Avanan said.
How to stay safe
1. Have a unique Email address.
2. Do not open any attachments without proper validation.
3. Don’t open emails voluntary emails.
4. Use Spam filters & Antispam gateways.
5. Never respond to any spam emails.