As of now you can easily prevent spammy and bots’ massages on your networks using CAPTCHA option.
It is available both for Ning 2.0 and Ning 3.0 platforms.
You can enable CAPTCHA in General Settings of your Network. Simply go to Social Site Manager section, if you are on Ning 3.0 or to Settings Network Details if you are on Ning 2.0 .
You can read more detailed info in our Help Center for both platforms here:
We use latest version of reCaptcha form Google which uses an advanced risk analysis engine and adaptive CAPTCHAs to keep automated software from engaging in abusive activities on your network. It does this while letting your valid users pass through with ease. Read more about Google CAPTCHA here - https://www.google.com/recaptcha/intro/index.html…
Even if you disable it, your new member will see CAPTCHA once when they're on registration page.