"Cannot open the file because the file format or extension is invalid" opening Office files


Upon further analysis of the files that have been submitted to us for investigation, the analysts

have determined that the files are encrypted with a private and public key.

Unless the private key is available, the files will not be able to be recovered.

The private key is more than likely held by the attacker.The premise of ransom ware such as this is

that if a person pays the ransom, a key is provided to unlock the files.

The best course of action is to clean up the malware and then restore files from a backup.


  We have identified the malware as a new family of ransomware



Definition Information:

    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.


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."





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




Security EssentialsMicrosoft Security Essentials  http://www.microsoft.com/security/pc-security/mse.aspx


Comments (39)
  1. Anonymous says:

    Any solution with this Cryptolocker yet? can we recover the files? have any tool from Microsoft to decrypt yet???
    I do need the solution on this now… 🙁

  2. Unfortunately until you can clean up the affected machine, restoring from backup will become corrupt as you have described. We are still working with our security teams and hope to have a signature available soon to detect the malware. We will continue to update this blog as new information becomes available.

  3. Anonymous says:

    If it happens completely randomly, does it happen more often to the same group of people? Perhaps an update malfunctioned?

    Reinstall Office? Try XLSX Open File Tool for recovery your documents (http://www.xlsx.openfiletool.com/)

  4. Anonymous says:

    Any solution with this Cryptolocker yet? can we recover the files? have any tool from Microsoft to decrypt yet???

  5. Signatures Updated. See Update section in blog…

  6. Anonymous says:

    go to
    delete all excel files

  7. Rayco says:

    I'm having issues with this as of today.  Has Crippled the file server.  

    We have good backups, but the files soon become "corrupt" when restored.

    I've ran several scans to no avail.

  8. Albi says:

    I have also run into the problem today. Restores seem futile and scans show nothing.

  9. Chris says:

    Ran updated scan.  It found nothing.

    Anyone else?

  10. tech4 says:

    I used security essentials after the update and was able to remove it. Stuck with a bunch of encrypted/corrupted files at the moment though :

  11. JDanker says:

    We're in the same boat with our file server.  If anyone works on a decryption, please let me know!

  12. kim says:

    We are in the same position.  We have removed the virus but are hoping that someone comes up with a decryption.  If someone does, please let me know as well.

  13. Nel says:

    We have a client that has no backup, pressures on!

  14. Abhi says:

    I have a client who started having the issue where they cannot open excel or word document that is store on the server. The network drive is mapped on users' computer. Whenever they try to open lets say spreadsheet, they get the same error as shown above under "More Information". When i restored the file from backup, it got corrupted again. However if i restored the backup by redirecting the location, it restored just fine and I was able to open it up just fine. I have not been able to isolate the location of corruption but this is really a pain. Any updates?

  15. Harry says:

    Any news on this? I just had the same problem…

  16. IT Guru says:

    Having the same issue here when opening Microsoft office extensions ending with x (eg. .docx, .xlsx) We are using the business version of 2013. Found a workaround to get these open by removing the x and using the old extension (eg. .doc, .xls) This is another nuisance in Microsoft's products and needs to be fixed. If you want us to be using this new format, you should have a fix for this! Hope this helps the ones the don't have a workaround yet.

    As for Microsoft, quit changing everything and just make sure it works, the amount of time and money we have spent troubleshooting these issues, we are going to start charging you for our time!

  17. Manish Garg says:

    Do we know how this exactly spreads?

  18. Sebastian says:

    I got the same problem as everyone. My Pc is clean. But the virus still got time to encrypt a lot of PDF, JPG, DOC, DOCX, XLS, XLSX Files.
    I tried a lot of tools for trying to repair, decrypt, recover thos files and none of them works.

    If anyone got a solution please post it !

    Thank you

  19. Shahinur says:

    Facing same problem on all office files and JEPG…Please let me know if get the solution anyone…

  20. Anonymous says:

    I got the same problem as everyone in this forum. Like Sebastian, my pc is clean, but all my files are still encrypted or corrupted. I have tried so many decrypter but nothing is working. PDF, DOC, DOCX, XLS, XLSX are corrupted. Please if someone find a solution, write it down.

  21. Tico says:

    Same here on a Windows 8.1 Pro w SSD. Started a couple of weeks ago. Some files get corrupted and others don’t – completely random.

    Have no issues on my older HP with Win7 and MS Office 2010. Been investigating this for 3 days with fingers pointing everywhere; Cryptolocker virus, Skydrive, new WIN8.1, etc.

    Have 3 anti-virus and none detected a virus. Ran and re-ran sfc /scannow countless times and nothing comes up. Tried one forum where they suggested to reboot with Memcheck – after hours of testing, no errors found.

    Extremely frustrated. Everything backed up on Egnyte is of no use since files uploaded are also corrupted or gets corrupted as soon as old version gets downloaded. Running out of options and sources to find solutions.

  22. Hamad Saber says:

    should we stop using Microsoft windows .more than 6 months with no solution only Microsoft can sale us bad product when it reach supports we will see them totally silent we will change our file server to linux

  23. Fadi Shaya says:

    Please let us know if you found any solution we are affected


  24. Fadi Shaya says:

    Please let us know if you found any solution we are affected


  25. Techy Guy says:

    Try changing the file extension to older version eg. .pptx to .ppt .docx to .doc

  26. Rahul acharya says:

    i have the same solution..when i recover my office file i cant open my file…. any solution please inform rahulacharya@gmail.com please! whatsaap number +97339517629

  27. Anonymous says:

    This problem spread world wide and still microsoft has no idea how to fix this?

  28. Ashok says:

    delete all excel file

  29. Steve Poison says:

    still no luck guys?

  30. collin says:

    is frustrating my docs are visible but cant be opened

  31. Robert says:

    We have this problem right now and its becouse of an virus/malware. Havent found the root of it all yet but it seems like a computer is the devil. All files that the user had read, write change access to was infected and encrypted via the Tor encyptement
    it says. The users are now disabled in AD and a restore is running. we found the users thrue searching for the extension in their home folders. thats the only Place were they are the only owners.

  32. bo hickey says:

    Firewall should protect from this no?

  33. mony says:

    i hope any one can fine any way to decrypt the files we need our files to be back as soon as possible

  34. edris says:

    any one tell me please how to solve this problem

  35. byt 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." when you transfer the file to other comp. same error message but files
    in the comp. can open without error

  36. Andrew says:

    Has anyone for the solution for this problem. Any way to repair those damage files ? Thanks heaps

  37. Adrin says:

    excel file not open because of Kaspersky antivirus what is the problem?
    sort it out

  38. genius says:

    open file with notepad++. search for ">" replace with ">" save as ".xml

  39. Thank you Microsoft support team; you helped me clean my PC 🙂

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