Text Message Code for access validation

Question

Hi guys,

I am looking for the best approch to validate authentication

Explain:

I would like to validate the computer (OS) that the user is using to login to the site and it is the first time login the site from such computer to pop a message "The computer you are accessing the site is not registered, please check your email and enter the code to authenticate this computer" prompt the user with code entry to validte and then, send either a text message or an email with a random code to be used in the prompting textbox.

 

What I am looking for is something the banks use to access personal or business account

when the first time accessing the portal it asks for a code sent to either email or text message depending how the user registration. 

 

Hope the above make sense. 

Any sample C# code would be very much appreciated 

 

Thanks