ASP Web Services Security

[malalation]

Hello guys,
I'm currently working on an ASP.NET project. The project requires an asp.net website and a vb.net application. The website and the application must be linked to the database, so I uploaded the database with the website on a web hosting server somewhere on the Internet and created a web service and uploaded it on the web server to link the database and the vb.net application. Finally, I added the web service as a reference in the vb.net project in order to make the required function calls.

The problem is that I want more security; I mean that I should make sure that no one can add my web service as a reference in his project and make the calls and change my data. I thought of adding a password and passing it to the web service as a parameter when calling a function and the web service checks if the password is correct then it will proceed, otherwise it will not execute the code, but it seams like a very primitive way of handling this issue. So, is there any other ways to do it?

[Hack]

Have a look at this MSDN article.