Security for webservice.

Hi all,

I need some information about web service security. For example I have created a web service which get sensitive information from my database and kept those in dataset. And finally I have deployed this web service in the IIS server. And this webservice will be consumed by some other application which lies in different server.

 In my webservice I have not provided any security. Now I want to give security to my web service. In this regard what type of security I should give and how can I do this security with one example pls?????

 Your help is always appreciated. 

Thanks,

Rahul