Block by useragent or empty referer

A stranger bot (GbPlugin) is codifying the urls of the images and causing error 404.

I tried to block the bot without success with this in the bottom of my .htaccess, but it didn't work.

Options +FollowSymlinks  

RewriteEngine On  

RewriteBase /  

RewriteEngine on  

RewriteCond %{HTTP_REFERER} !^$  

RewriteCond %{HTTP_USER_AGENT} ^$ [OR]  

RewriteCond %{HTTP_USER_AGENT} ^GbPlugin [NC]  

RewriteRule .* - [F,L]

The log this below.

201.26.16.9 - - [10/Sep/2011:00:06:05 -0300] "GET /wp%2Dcontent/themes/my_theme%2Dpremium/scripts/timthumb.php%3Fsrc%3Dhttp%3A%2F%2Fwww.example.com%2Fwp%2Dcontent%2Fuploads%2F2011%2F08%2Fmy_image_name.jpg%26w%3D100%26h%3D65%26zc%3D1%26q%3D100 HTTP/1.1" 404 1047 "-" "GbPlugin"

Sorry for my language mistakes

Thank you, Vera

Source: Tips4all