Alert – Guidance Concerning “Petya Ransomware”

What is the purpose of this alert?

This alert is to provide you with guidance concerning the ransomware issue being discussed broadly in the press starting on Tuesday, June 27, 2017, and causing a large volume of customer inquiries.  This ransomware is being described by the press and security researchers as “Petya Ransomware.”


Microsoft’s antivirus software detects and protects against this ransomware. Our initial analysis found that the ransomware uses multiple techniques to spread, including two which were addressed by a security update (MS17-010) previously provided for all platforms from Windows XP to Windows 10.

As a general precaution, customers should exercise caution when opening unknown files. We are continuing to investigate and will take appropriate action to protect customers..

Malware Detection

Windows Defender, System Center Endpoint Protection, and Forefront Endpoint Protection detect this threat family as Ransom:Win32/Petya.Ensure you have a definition version equal to or later than:

  • Threat definition version:
  • Version created on: 12:04:25 PM : Tuesday, June 27 2017
  • Last Update: 12:04:25 PM : Tuesday, June 27 2017

In addition, the free Microsoft Safety Scanner is designed to detect this threat as well as many others.

Those with a solution from an antivirus provider other than Microsoft should check with that company.


Three specific steps customers can take to mitigate against new ransomware: 

  1. Ensure you have the latest security updates installed
  2. Ensure you have the latest AV Signatures from your preferred AV vendor
  3. Do not open email/attachments from unknown/untrusted sources

Note:  these are good security defense-in-depth recommendations that may prevent being infected by this ransomware, but these steps alone do not ensure against infection.

Additional Resources

More Information

When new information is available that we can share, we will send a new security alert.

Regarding Information Consistency

We strive to provide you with accurate information in static (this mail) and dynamic (web-based) content. Microsoft’s security content posted to the web is occasionally updated to reflect late-breaking information. If this results in an inconsistency between the information here and the information in Microsoft’s web-based security content, the information in Microsoft’s web-based security content is authoritative.


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