500 sign ups in one day...Why spammers, why?!?

Is it normal to have so many bots and spammers registering for my site? Is it a good indication that my website is showing up on the SEO? Or is my site just not well protected? I mean, I know every website with a good amount of traffic gets about 100 spammers a day. But 500 in one day, come on. Someone please explain this to me.