[Darth-Apple]

I think another easy way to protect is a captcha with a simple instruction like...

Who is the founder of Microsoft? (write a _ between names like Jonh_Smith)
So, instead the bot could google Bill Gates and paste it is nearly imposible it can follow the instructions to write Bill_Gates instead

That's a good one. The only way a bot is getting through that question is if it is human-assisted.