We have identified the malware as a new family of ransomware
Latest public Endpoint AM defs: 1.157.1542.0 (Expect several hours later for 1.157.1559.0 or higher)
Latest Prerelease AM defs: 1.157.1542.0 (Expect several hours later for 1.157.1559.0 or higher)
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.
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."
It's recommended you update the definitions in your antivirus software and run a complete scan of the affected machine(s).
When opening binary Word (.DOC) files that are attributed with this issue, Word does not know how to open, so you receive a dialog for File conversion as shown below.
We've had reports of it affecting Word documents, Excel files, PowerPoint files and Access databases.
Other Support Blog links
Microsoft Security Essentials http://www.microsoft.com/security/pc-security/mse.aspx