Spam

I am working with wordpress multisite. I have pretty much knowledge in wordpress but not enough. I never able to fix the wordpress spam issue. Ok my question is in my wordpress mulitsite I want user to create account and blogs but how can I stop spam registration and creating blogs. any plugin suggestion or something? also if you have any plugin for comment + bbpress + buddypress spam. overall the spam. I can not buy any premium plugin for every single bolg of my site. right? so please suggest Thanks :slight_smile: