If there is high traffic on your website from different IP addresses with one and the same User Agent, you can restrict them by blocking. For this, you need to edit your .htaccess file and add the below rules:
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} UserAgentName [NC]
RewriteRule .* - [F,L]
Here replace UserAgentName with the actual name of the User Agent. For example, for blocking a User Agent named Textbot, you should add the below code:
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} Textbot [NC]
RewriteRule .* - [F,L]
Add them at the start of the .htaccess file. For blocking more than one User Agent (e.g. named SCspider, Textbot and s2bot), add the below code:
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} ^.*(SCspider|Textbot|s2bot).*$ [NC]
RewriteRule .* - [F,L]
For blocking the requests from machines with missing User Agent, add the below rules in your .htaccess file:
RewriteCond %{HTTP_USER_AGENT} ^-?$
RewriteRule ^ - [F]
In this way, you can clock a User Agent in an .htaccess file.
Also Read:
How To Change Document Root Using .htaccess File?
Steps to Enable Password Protection for .htaccess
