If you are running Antivirus software we recommend adding the entire BO3 folder to your antivirus Exception List. The folder is commonly found at C:\Program Files (x86)\Steam\steamapps\common\Call of Duty Black Ops III
For Comodo Users select Settings -> Advanced Protection -> Miscellaneous -> Detect Shell Code Injections [Exclusion] and add the entire BO3 folder to the exclusion list.
For Bullguard Users you will also need to go to Settings -> Main -> and uncheck self protection.