Plus, they can't spider the forums anyway, as it's disabled in robots.txt. You'll notice there are never any forum threads appearing in Google search results.
That said, I just discovered a search result in a service called BoardReader -- looks like they are rude and ignore rules in robots.txt so that they can index forums! That's just naughty....! If a site owner says "no, you can't search this", that should be respected. So many arseholes on the web.....
Hmm. A competently designed spider wouldn't have a huge problem with that, but then again, a competently designed spider would respect robots.txt, too.
I guess if BoardReader becomes a problem you can always ban then explicitly. They're at least ethical enough to have "BoardReader" as their user-agent. For now, anyway.
they probably use such things to track down those naughty people who like to talk about overthrowing governments... after all if you can just block such searches from reading your conversations of world domination, it wouldn't be safe.. and well.. on a more serious note, there are a number of subjects on which people try to hide their involvement in.. you see them being arrested en mass from time to time for bad things they posted in "secure" locations.. there are a lot of perverts and sickos on the net..
The Pan Inter Teratoids came in a red flying saucer from above (A). There were strong convection currents below their spacecraft.
Then it stopped and became stationary, seemingly contracting and expanding. (B)
And... they're spying on us!