Excessive access from external source, using an empty / blank user_agent string; via multiple IP addresses.
Legitimate web browser traffic would normally communicate various standard user agents to Apache.
Solution: Use .htaccess to block empty user_agent as follows…
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RewriteEngine on # BEGIN block access for empty user agents - 403 error RewriteCond %{HTTP_USER_AGENT} ^$ RewriteRule ^(.*)$ - [F,L] # END block access for empty user agents |