For apache servers, htaccess is the best tool stopping bot traffic cold.
Benefits:
little CPU and little memory being consumed versus full-blown call to the server and database
Faster server responding time and no unnecessary upgrade to server hardware simply because bot traffic has consumed major part of CPU and memory.
Two ways of doing it, if the server is powered by WordPress
1. manually – time consuming
2. using a WP plugin such as All In One WP Security.
Further info and read:
https://www.google.com/search?q=using+htaccess