If you offer free membership registration on your site then it can be affected by spam signups (bots completing the registration form).
You can enable Google reCAPTCHA on your member’s registration form if your site gets a lot of spam signups. Google reCAPTCHA will cut down all the spam signup attempts on your membership registration page.
Enabling Google reCAPTCHA
Go to the Google reCAPCHA settings tab from the main eMember settings menu. Then fill in the API keys to enable this option.