how many forums in this world?

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A few days ago, i was chat with my friend and talked about software. Than, we discussed the forums which content a software we looking for. start searching with google, and surprisely so many forums i can get the software. It's not possible for me to join all forum, just because 1 software. I wonder how many forums in this world? Anyone can count it? Until now i just join 4 forums include mylot-mylove discussion forum :)