Mark Ratledge on "spamming bots - option_com=k2, htacces changing"

Hello, my site is getting slow because of spamming bots like:

38.87.46.132 - - [06/May/2016:19:34:40 +0200] "GET /?option=com_k2&view=itemlist&task=user&id=465707 HTTP/1.0" 200 11955 "-" "Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:34.0) Gecko/20100101 Firefox/34.0"
155.94.179.172 - - [06/May/2016:19:34:24 +0200] "GET /component/user/?task=register HTTP/1.0" 404 9092 "http://www.example.com/index.php?option=com_user&view=register" "Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:34.0) Gecko/20100101 Firefox/34.0"
155.94.179.172 - - [06/May/2016:19:34:22 +0200] "GET /index.php/component/user/?task=register HTTP/1.0" 301 670 "http://www.example.com/index.php?option=com_user&view=register" "Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:34.0) Gecko/20100101 Firefox/34.0"
38.87.46.132 - - [06/May/2016:19:34:40 +0200] "GET /?option=com_k2&view=itemlist&task=user&id=465707 HTTP/1.0" 200 11955 "-" "Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:34.0) Gecko/20100101 Firefox/34.0"

I've tried to block them by .htaccess, but without any sucess :(

<IfModule mod_rewrite.c>
RewriteRule ^component/k2/itemlist/user/d* - [F,L]
RewriteRule ^option=com_k2/ - [F,L]
</IfModule>

Maybe you have solution how to block them? I'm using plugin WP Security.