Patrick O'Neill writes: A common configuration mistake in Apache, the most popular Web server software in the world, can allow anyone to look behind the curtains on a hidden server to see everything from total traffic to active HTTP requests. When an hidden service reveals the HTTP requests, it's revealing every file—a Web page, picture, movie, .zip, anything at all—that's fetched by the server. Tor's developers were aware of the issue as early as last year but decided against sending out an advisory. The problem is common enough that even Tor's own developers have made the exact same mistake. Until October 2015, the machine that welcomed new users to the Tor network and checked if they were running up-to-date software allowed anyone to look at total traffic and watch all the requests.