AHMN48 - Wednesday, February 22, 2017 3:25 PM
That sounds like ransomware. If I am correct, your .bak file will be corrupted beyond repair unless you pay money to get the decryption tool and even then there is no promise that it can get decrypted.
Do you have any offsite backup or tape backup or anything?
Unless you are willing to pay money, you likely won't be getting that database back.
The above is all just my opinion on what you should do.
As with all advice you find on a random internet forum - you shouldn't blindly follow it. Always test on a test server to see if there is negative side effects before making changes to live!
I recommend you NEVER run "random code" you found online on any system you care about UNLESS you understand and can verify the code OR you don't care if the code trashes your system.