TrojanDownloader:O97M/Donoff

Detected by Microsoft Defender Antivirus

Aliases: No associated aliases

Summary

Microsoft Defender Antivirus detects and removes this threat.

This threat uses an infected Microsoft Office file to download ransomware and other malware onto your PC.

It can arrive on your PC as spam email attachment, usually as a Word file (.doc).

As part of our continued efforts to tackle entire classes of threats, Office 365 client applications now integrate with Antimalware Scan Interface (AMSI), enabling Windows Defender ATP and other security solutions to scan macros and other scripts at runtime to check for malicious behavior. Learn how this integration exposes malicious intent even with heavy obfuscation: Office VBA + AMSI: Parting the veil on malicious macros.

Use the following free Microsoft software to detect and remove this threat:

Windows Defender for Windows 10 and Windows 8.1, or Microsoft Security Essentials for Windows 7 and Windows Vista
Microsoft Safety Scanner

You should also run a full scan. A full scan might find other hidden malware.

Prevent malware infections from spam emails

For enterprise users:

Follow the appropriate Exchange Online Protection instructions to suit your business needs.
Learn about how Office 365 can help you block spam using machine learning. See First look at Advanced Threat Protection: new tools to stop unknown malware & phishing attacks for details.

Be aware of the dangers in opening suspicious emails. Don't open email attachments or links from untrusted sources.
The Microsoft SmartScreen filter can also help detect spam. It’s built-in and enabled by default in Microsoft email programs.
Submit spam and non-spam messages to Microsoft for analysis.