This article describes how to use cPanel's IP blocker tool to prevent specific IP addresses or domains from accessing your website. You can use this feature to block visitors who use a large amount of bandwidth.
Step 1: Login to the cPanel and go to IP Blocker.
Step 2: Under "Add an IP or Range", please enter IP address or domain name you wish to block.
Step 3: Click the Add button to block the IP address
Note : On VPS and Dedicated servers IP's can be blocked using iptables.