Right. Search engine crawlers, I think scan forum content for updates quite frequently. You can also see the direct results if you search (e.g., "google") something and find any recent forum posts come up in the results. That wouldn't work without the crawlers.
There was a forum "member" recently also, who was actually a spam bot, who I reported. They had accumulated dozens of posts which were all robotic posts - many of which would simply repeat previous content in the thread. Some would combine content from more than one post in the thread, and especially for the long threads, it could be very hard to detect to the casual observer! Other robo-posts, however, were pretty obvious. I'm sure the technology will only get more sophisticated though, so hopefully we'll not lose sight of whose an actual person versus algorithmically produced and contributed content.
Be vigilant, (human) 986forum denizen!