What is the default SSIS Account that is used in SSIS packages. 

In one of my packages I have a Data Flow task that creates a flat file. A BAT file later runs and creates a file based on information in that .txt file. If I execute the .BAT in Windows Explorer it runs fine. When SSIS tries to execute it I can see the CMD window open and it tries to access the txt file and isnt able to. Says "Unable to access nameoffile.txt"

I assume the issue is that the permissions are probably inherited by the SSIS user account so I am trying to figure out which account that is.