Tons of bad bots hit our servers every day and I have tools to instantaneously block them (i.e. modsecurity and a C++ tool of my own.) These block the bots so no data is sent back and they are banned on my firewall so any extra hit is immediately turned down. On one of my server (small one!) I get over 20 such blocks (IPs) per day and that server only gets ~3,000 hits a month.
Now, the IP block is temporary mainly to avoid crowding my firewall (1,000's of IPs in your firewall will make it really slow!)
However, I'm wondering now... What do you do on your end? Block everything at once or send the bot to la la land with a redirect? I'm thinking that I could have a tiny HTML page with nothing on it (you know, something like a title and a body which say "Thanks" and voilà).
Which do you think is best? I've seen that redirections did not seem to deter any robots so firewalling them has been my best solution so far... but I was wondering what others do in this situation?