BuddyPress.org

(with no real Search here, have no idea how many times this has been asked/answered)
Relatively new WP/BP Admin, I’m running BP 1.5.5 and now getting regular “registration spam”, i.e., “people” creating an account with no intention of using the site except to display their stupid but innocuous things like EU Lotteries with a few links sprinkled in. I haven’t seen anything horrible yet, and I’m deleting manually when I can.
(Note that this is not Comment spam; it’s Registration spam)

I’m surprised that the basic BP install does not include a Captcha-type function to help deflect these automated registrations, if that would even work.

Q1: What are best solutions to stop this? Is there an “approved” plugin to install?

Q2: What is the real danger here? Most of what I see is worthless, and I wonder if anyone even sees this stuff. What is the real negative impact?

Thanks for advice.