If your Mighty Network is public, you have the option to decide if you want member posts and profiles to be seen by search engines like Google.
You can find this setting if you go to Network Settings > General Settings and scroll down until you see Search Indexing under your privacy settings.
By default, this toggle will be switched "on" so that your Mighty Network is crawled and indexed by search engines like Google and Yahoo. This means that all pages of your Mighty Network will be visible in search results.
If, however, you want to keep your network public, but make it so that member posts and profiles aren't seen by the search engines, all you have to do is switch the toggle to "off." Your Landing Page will always be searchable, but all other pages of your Mighty Network will not be indexed by the search engines.