We don't know how or why yet, but the world's online encyclopedia, Wikipedia, has gone down for the count.

Wikipedia only went down a few minutes ago, according to the Twitter stream, which is already pumping out dozens of tweets per minute about the outage. There is only a "Server Not Found" message from our end. Wikipedia.org is up, but most — if not all — of the language-based encyclopedias are down, including the English one.

Unlike Twitter and Facebook, there isn't a stream to check the status of the web's de-facto information hub. We'll continue to investigate what is happening and let you know as soon as we find out.

Update: Overheating in the European data center and broken DNS resolution of Wikimedia sites affected Wikipedia across-the-board. From the Wikipedia Tech Blog: