Block web page requests from robots with empty user agent

To block any request to the server from an empty user agent, use the below code in .htaccess file

RewriteEngine On
RewriteBase /
SetEnvIfNoCase User-Agent ^$ bad_bot
Deny from env=bad_bot


This will give a 403 response to the spammer who try to access the site with out any valid user agent.
The response will be like
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HTTP request sent, awaiting response... 403 Forbidden
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