its a good technique to Restrict user to view your website , this task can be done with the help of checking of user's IP Address and match with our database and if user get found under
that IP then you can set Denied Access to them .
But in this case you need a Live IP Address database,
there are so many website are there they are provides free IP Address database range .
and with the help of that u can Denied user.
here are the List of free IP address database sites
Simply download that.
1. Create one IP check function
2. take user Ip address
in ASP : - Ip =Request.Servervariables("REMOTE_HOST")
in C# : - String ipAddress = (Request.ServerVariables["REMOTE_ADDR"]);
3. then check if user's Ip address is there in you'r database , depend on that
you can prevent user.
hope it will helps you,