Because your Visual Basic .NET application is typically made up of calls to Visual Basic .NET–provided functions and methods such as FileOpen, Kill, Shell, and Show, all these functions internally check to see whether your code has sufficient permissions to perform the requisite action. If sufficient permissions have not been granted by the .NET code-access security system, a security exception is thrown and the action is not taken. There is nothing you need to do to turn on code-access security in your Visual Basic .NET application. It’s on by default.