How to exclude sensitive data from app.config

Hi, I have a question when creating a new data connection for my application on WinForms.

When I'm creating the connection it gives me two options, the first is:

No, exclude sensitive data from the connection string. I will set this information in my application code.

and the other is:

Yes, include sensitive data in the connection string.

I want to know how can I use the first option and not store the password in a file so anyone will be abble to see it, how can I set the password in my application code supposing that the user name and password may differ from computers so I cannot set one default user and pass?

Thanks.