Facebook Traffic And Registering

Hi there,

I don't know if I'm posting at the right place but I want to know if this has happened before to cs-cart users. Yesterday at about 12pm I check google analytics and I started to get a very big amount of visits coming from facebook. (I got over 1600 visits from 12pm to 12am). I have a multivendor site with captcha and getting people that I think are bots registering. I have a facebook like box on my main page and it went from 272 to 316. Has that ever happened to someone? How do I stop this because I think they are bots. Please give me feedback.