Blocking a specific IP (visitor) from accessing your website is always a great feature. This is extremely effective to block malicious or unwanted users from accessing your website.
The IP Deny Manager helps you block a specific IP Address from your website. You can find the manager in your website's Control Panel.
In there, by using the Block an IP Address section you can block unwanted IP's and leave a note to the block (great for remembering why this specific IP was blocked if it's only temporary).