How websites like Facebook are protected against bot without any captcha

Question

How websites like Facebook and Twitter are protected against bot during registration? I mean, there\'s no captcha at all on the signup form?

I want to create a signu

Answer 1

Well you can always deploy hardware solutions as well to create Layer 4-7 firewall rules. You can create specific rules to look for the well known agents of bots crawling the web. However to stop newly created bots you need to know what agent they are using for the bot.