I have many large forums about a specific topic... however I also have an "off-topic" forum that I want to disallow from the search engines using robots.txt.

I am running vBulletin and the link to the off-topic forums is
/forums/forumdisplay.php?f=9

If I disallow this in robots.txt... will that disallow just this off-topic forum or will it disallow all forums because google will just disallow all forumdisplay.php links, regardless of the ?f=9

Hope that makes sense. Thanks.

Couldn't you just make it so guests can't view those forums? Spiders are treated as guests, and can't view it if disallowed.