There are 5 features offered on a Ning Network that help prevent Sign-Up Spammers. To set your options, access the features via: My Network/Members/Controls

You can approve all new Members. This definitely helps in the prevention of Sign-Up spammers joining your Ning Network. You may not catch all of them, but most will give you good indicators that they are spammers. If you see repeated words like "i tell you later, i tell you later", or "i'm a good girl looking for love", etc... you can bet your bottom dollar, these are spammers. And of course goes without saying, Do not approve these accounts.

If you do not want to "Approve Members", there are 4 other features that will help prevent Sign-Up Spammers:

• Require new members to verify their email address - I advise turning on this feature for all Networks.
• Fill out a captcha
  • An image containing words that users must correctly identify.
  • I advise turning on this feature, due to most auto-spambots cannot enter a captcha correctly, since it is a never changing "image".
• Answer the sign-up quiz
  • Create a quiz question that new members must answer correctly to join.
  • You can really get clever on the sign-up quiz question. I saw one where a Network Creator asked "Are you a real person?" and he set the default answer to "No". This will catch a lot of spambots, no doubt.
  • Definition: A spambot is an automated computer program, or, more rarely, a script, designed to assist in the sending of spam - - and joining Networks for the same purpose in mind, including dropping links to illegal sites.
  • Another great way to utilize this feature: add a question that only applies to your type network. Add a question that members of your site should know, if they are interested in joining your Network. A great example: A Ning Network for Golf may ask a question like this, "Would you rather have a Birdie or a Bogey?"
• Spam Prevention - Automatically suspend suspected spammers
  • I'm not sure what algorithm or criteria is in place for suspending suspected spammers.
  • Please let us know your experience, if you know more about this feature.

Here's a screen shot of your "Prevent Spammer" Controls:

Perfect Example - - Just had this spammer join JenSocial (August 10, 2010), and about the 7th one today. BTW, I have not set a question for the Sign-Up Quiz yet. I will very soon!