how can i protect my website ?

McAfee?

Without any information, how is anyone supposed to answer it?

Here's the answer with as much effort as you put into the question:

Secure the server (whatever OS it may be) and the software (whatever it too may be).

If you want to stop your site from appearing at search engines, you can use robots.txt, but if you need to stop repetitious requests or DOS like spamming/attacks, then it is more of a network/server issue.
Using robots.txt will not stop your site appearing in search engines, only those who choose to comply with the robots.txt standard.