Is it possible to stop "newcomers" from posting their problem inside someone else's thread, that happens to cover the same problem?

Currently the "Websearch" contamination has a couple of these in the Windows OS and/or Misc. Software and Utils.

Perhaps check the number of posts: if "1" do not let this person reply, but let them only open a new thread.

Well, I don't think that's a too good an idea.
Just because you're new doesn't mean you can not answer a question.
Besides, all needed to get around it is to post a new thread in the Newcomers welcome...

And I can't say I've seen too much of the problem.

In that case, perhaps inform newcomers on their welcome-screen, that they should NOT open a new thread inside someone else's.

Can't remember "the Newcomers welcome..."

You can also use Report this post to moderator thing within the new post that should be a new thread.
You will then be prompted to enter a reason why. After that the moderator(s) for that forum will get a message saying what the problem is, and then we can split the thread into 2 threads.

I thought that was the point, try to find an answer inside an existing thread, if you can't, then post to it adding any relative info, thus bumping the thread up to get attention. Its better than having 500 threads about the same exact problem.

I agree with SB on this one. All the duplicate name threads tend to be ignored by me unless I'm looking to delete one of them.

Just clarifying that I too agree with StormBringer and LNCPapa.

It also makes it easier for people to compare their HiJackThis logs, and see what needs to be done...

Well I disagree , sortof.

I think normally if you have a similar or same problem that wasn't resolved by following a thread it is ok, and infact condoned, to post in that same thread. But where I disagree is when 1 person's problem hasn't been resolved, and somebody hijacks the thread and puts their own problem in, in this case (I think, I don't read any of those hijackthis threads) having all those logs and people not getting problems resolved and then getting confused in all of the cross talk, its just undesirable. IMO.

Perhaps if everyone makes a consious effort to put the name of the person they are replying to in bold it would eliminate some confusion.

Well, in the case of those hijackthis threads, the problems are usually not the same, the only thing in common is that they ran hijackthis and generated a log. Those threads almost always go unanswered because of the fact that no one wants to sort through the log to find every entry that might be bad. Also, when you have several people posting completely different logs and don't really give any reasons for their concern, it gets difficult to answer even one, muchless cover the entire thing with a resolution.

The main point I was trying to make is that when you have the same problem as someone else, add it to an existing thread, its very likely that the eventual resolution may solve your issue too. It will also help others find a resolution in the future.

As for the replies confusion, thats what the quote function is for, just eliminate the bulk of the quote as to not have to repost their entire post, then make your reply. It takes a few seconds of effort but anything worth doing takes at least some effort. I know thats a huge concept for some people in a "point and click society" but I think its possible for people to grasp that concept.