some hackers are hacking my sites again and again
can u tell me how to prevent those hackers from hacking my site...??

I am going to go out on a limb and assume that you manage your site yourself, possibly on a shared hosting account. Work with a systems administrator at your hosting company to buckle down your server. Explain to your host that it is in their best interests to devote time to helping you, since it is compromising their network as well.

oh that happened to me once, knocked down 10 of my sites. I moved to a better server.

If you are using a content management system like Joomla or Drupal, or a blogging/CMS platform like Wordpress, check out their websites for modules and plugins to improve security. I use WP on a few of my site and have BulletProof Security installed. The plugins protects a website from XSS, CSRF, Base64_encode and SQL Injection hacking attempts.