How to secure web application.

Question

Hi all

I am developing a finance application which will be use to transfer money, and application will be publicly available on internet, some agent user will have their credentials to access some parts. I have only used form authentication and nothing else for security point of view.

Is it good enough for security or should I use something  more methods to secure my site.

Please advice me and give me some more point to secure the application.

I have developed my application in asp.net.