UPDATE:
We have identified the malware as a new family of ransomware
Definition Information:
The signatures are now updated. You should be able to use Safety Scanner to detect and clean it. It does NOT clean your documents, so you will want to restore from a backup after cleaning the malware from your system.
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More Information:
We are currently investigating an ongoing situation where users may encounter an error when trying to open Office documents.
The error can happen opening any Office file type, not just Excel files as shown in the image below. The error says:
"Cannot open the file ... because the file format or extension is not valid. Verify, that the file has not been corrupted and that the file extension matches the format of the file."
With PowerPoint binary files (.PPT) , you will see a dialog similar to the following screenshot. We don't have OOXML samples yet but will post images once we have these.
Other Support Blog links
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Microsoft Security Essentials http://www.microsoft.com/security/pc-security/mse.aspx
Signatures Updated. See Update section in blog…
Yes. Security Essentials should have these definitions. Just make sure your definition version matches the ones listed in the Updated section.
It also is affecting Powerpoint
Will Security Essentials be updated with these definitions?
What about the files? once the ransomeware removed, will we be able to reopen them?
"Excel cannot open the file ‘data.xlsx’ because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file." ,, only this file others are okay,,,