I guess this isnt a possible solution, so I am planning to set the permission of the forum pages, to only allow members only. Visitors wont be able to view the content. But I had to provide a way that google can still index the content, for the member pages.
So I found this topic:
http://www.inceptor.com/blog/2010/1...tion-page/ 1. Google’s First Click Free Program
Google recently introduced a new program for publishers of content that is protected by a login page. Called “First Click Free”, participating publishers allow the Google crawler to index their subscription content, then allow users who find one of those articles through Google News or Google Search to see the full page without requiring them to register or subscribe. The user’s first click to the content is free, but when a user clicks on links on that free page that lead to additional restricted content, your website can show a registration request / login page.
Also, thanks to an update to the FCF program, you can now limit users to no more than five pages per day without registering or subscribing. If you’re a Google user, this means that you may see a registration page after you’ve clicked through to more than five articles on a given website using First Click Free in a day. As Google says, “We think this approach still protects the typical user from cloaking, while allowing publishers to focus on potential subscribers who are accessing a lot of their content on a regular basis.” The Wall Street Journal is a high profile case where this FCF program is being used.
How it would work
• You enroll in the FCF program and allow Google to crawl all your content behind the registration page.
• You could selectively prohibit certain documents from being published in this manner by using the “no index” tag and/or the robots.txt file (this needs to be confirmed).
Benefits
• Makes restricted content available to the public in full (using Google Web Search no partial viewing of documents is possible through FCF).
• Restricts how much content a user can view in one day to five complete documents.
Issues
• Makes restricted content viewable only through a search on Google, not to general website visitors.
• Users can view up to five complete documents each day – this might be too many documents for you.
• Content pages that contain restricted or sensitive information would each need to be protected using the no index tag/robots.txt method mentioned above. If you have a lot of this type of content, this may turn out to be a prohibitively large amount of work for you, and it would need to be done in advance of enrolling in FCF.