BuddyPress.org

You could also try some WP plugins that add additional hidden, input fields to the registration form:

-Invisible Defender – https://wordpress.org/extend/plugins/invisible-defender/

-NoSpamNX – https://wordpress.org/extend/plugins/nospamnx/

Chances are a spam bot will fill these input fields in, and thus these plugins will block these submissions.

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I’ve been meaning to give this a shot, but I haven’t tried it yet because I don’t need the extra layer of protection (right now anyway)!