Private Forum being indexed by search engines?
 

We recently purchased a license and in process of setting up our forum. This forum will be setup as a private forum and by invitation only. I have read the posts about how to make the forum private. My question is, by setting the right permissions and making the forum private, will it prevent search engines from indexing the content? Although, most users are utilizing forums for SEO purposes, we are trying to accomplish the opposite effect.

Any suggestion is appreciated.