Everything, Everything

No, nor was I. Google pretended to offer broadband via the sewer system, which wasn't particularly funny, and IIRC one of the councils in the south of England have actually run cables through the sewers as a backup connection. I did come across a better one where Maria Sharapova's website had a Cross Site Scripting (XSS) error that allowed you to see that she was now Cisco Certified, and to make it more plausible there was a XSS attack on a Cisco search engine that allowed you to read a similar article on Cisco's site. Vaguely funny, but the problem with XSS attacks like that is that the URLs tend to be long and contain obvious signs of JavaScript. It's much better when they get to post content onto the site for all to see when accessing "normal" URLs. I did that last week during a training session, getting the instructor to see a "Hello World" JavaScript alert popup while he was trying - and ultimately failing, because the server was escaping the pipe symbol - to demonstrate another form of attack. The best idea for an April Fool's was one I read on Scott Adams' blog that was performed on him several years ago and apparently took him years to work out how they did it. They'd called one of his telephone numbers and also called another number of his, so that when he answered the phone all he heard was his own answering machine asking him to leave a message. It obviously works best if you withhold your number.