However since Winzip and StuffIt are the most popular, we will assume you will use either one to compress and decompress your own files. If you download a compressed file from a website or file library that ends in an .exe extension, take note that although the file is compressed, it's typically a file that will install a program onto a computer. His intentions were to disable the computers of the online service's users so much that they wouldn't be able to connect for days. In his mind, the loss of connection meant loss of revenue for the online service. Although the malicious code that this person generated may have worked for a small percentage of users, sufficed to say, the online service continued on and still exists today. Even though you may use Windows XP or Vista, batch files can save you tons of time by automatically starting multiple programs and performing different tasks at the single click of a button. They don't require any extensive programming background and they don't need to be encrypted with some weird, expensive compiler. We may need a word processor that can convert a document into an HTML page or PDF document. We may need a calculator that solves geometric problems. Or we may need a multimedia tool that lets us create our own videos as well as watch them. These capabilities aren't included with new systems, but there's no reason why we can't exploit the tools that we're given to their fullest. Some of the more popular ones are Windows Vista, Mac OS X, ZETA, IBM, Unix, and Linux. But even still, operating systems have extended onto to non-computer devices such as game consoles, portable music players, and PDAs. Regardless of the device, the operating system installed onto it serves the same purpose across the board: to enable user-to-hardware communication. Okay - we're assuming that the reasoning behind hiding extensions is a "user-friendly" one because we just can't come up with any other reason for hiding them. No harm could ever come from seeing an extension, but plenty could be learned from it. Fortunately you have this article to guide you through some of the most common extensions that you'll run into.