How to completely hide my forum from search engines?

[EarthDog]

I need to hide all my forum topics from all search engines?

How i could accomplish this?

 

[opentype]

The only reliable way: remove guest access. 

Other than that you can only suggest search engines not to crawl your forums in the robots.txt

User-agent: *
Disallow: /forums/

(This is an example. I don’t know your site URLs)

[EarthDog]

Thank you.