Leggevo questo topic visto che stavo per crearne uno anch'io...
Ti consiglierei di aggiungere anche questo pezzo di codice al tuo file .htaccess, dovrebbe tenere fuori quasi tutti i bot maligni.
Codice:
# BLOCK USER AGENTS
RewriteEngine on
RewriteCond %{HTTP_USER_AGENT} AhrefsBot [NC,OR]
RewriteCond %{HTTP_USER_AGENT} spbot [NC,OR]
RewriteCond %{HTTP_USER_AGENT} DigExt [NC,OR]
RewriteCond %{HTTP_USER_AGENT} Sogou [NC,OR]
RewriteCond %{HTTP_USER_AGENT} MJ12 [NC,OR]
RewriteCond %{HTTP_USER_AGENT} majestic12 [NC,OR]
RewriteCond %{HTTP_USER_AGENT} 80legs [NC,OR]
RewriteCond %{HTTP_USER_AGENT} SISTRIX [NC,OR]
RewriteCond %{HTTP_USER_AGENT} HTTrack [NC,OR]
RewriteCond %{HTTP_USER_AGENT} Semrush [NC,OR]
RewriteCond %{HTTP_USER_AGENT} Ezooms [NC,OR]
RewriteCond %{HTTP_USER_AGENT} CCBot [NC,OR]
RewriteCond %{HTTP_USER_AGENT} TalkTalk [NC,OR]
RewriteCond %{HTTP_USER_AGENT} Ahrefs [NC]
RewriteRule !^robots\.txt$ - [F]
# BLOCK BLANK USER AGENTS
RewriteCond %{HTTP_USER_AGENT} ^-?$