Avast Decryption Tool for XData will decrypt files that have been targeted by the XData ransomware, which is a derivative of the AES_NI strain of ransomware. All the Avast Decryption Tools are available in one zip here.
XData utilizes the Eternal Blue exploit to spread itself and infect other machines.
It will add the ".~xdata~" extension to any encrypted files and within one of those encrypted files, the text file "HOW_CAN_I_DECRYPT_MY_FILES.txt" will be found. This particular file will contain the ransom note that will be like the example shown in the screenshot below.
XData also creates a key file with a name similar to [PC_NAME]#9C43A95AC27D3A131D3E8A95F2163088-Bravo NEW-20175267812-78.key.~xdata~. You will find it listed in the following folders; C:, C:ProgramData, and Desktop.