Microsoft Defender for Office 365 (formerly known as Office 365 Advanced Threat Protection - ATP) is a service from Microsoft that protects users from malicious threats posed by email messages, URL links and collaboration tools.  

 

The protections cover 3 areas:

• Safe Links – It protects you against malicious URL embedded in your received emails by scanning and re-writing the URL. This helps you against phishing attack
• Safe Attachments – it protects you against zero-day malware which cannot be detected by traditional anti-virus tools
• Protection for SharePoint/ Teams/ OneDrive – extends the above protection to your cloud storage