Spam Bots

Hi Guys,

I am working with an educational institute where kids from grade 1 to 12 have their own WordPress blogs. We are using multisite (WordPress Network) setup.

Recently we shifted from self hosted servers to AWS and have been under attack by bots (comments spam and brute-force login attempts). I tried implementing CAPTCHA codes for the blogs, but we noticed it becomes annoying and probably difficult for the elementary kids as those captchas can sometimes take more than one try.

Is there any other way or plugin which I could use, where kids would not have to fill in CAPTCHA code and still we do not have these spams attacking our server.

Also, many times there are so many bots that our CPU utilization goes to 100% and apache stops responding.

Thanks in advance.