Because some programs share common files, errors can also occur when these shared files are not up to date. For instance, let's say that Program A is already installed on a computer and it's working just fine. Then let's say that the user of that computer downloads and installs Program B. Program B uses a file that Program A installed much earlier, but when Program B is run, errors popup. A programmer chooses one language by a simple preference. Each of these languages differ by the way they communicate with a computer however, and the commands that they follow are very specific. Not a single command of one language can be interchanged with the commands or language of another. But all of them can be used to control a computer. If a single printer is available on only one computer in the network, every connected PC can send documents to it and print them out. Kids will enjoy the ability to play multi-player games and adults will enjoy the ability to blast a single message to everyone at once or maintain a group schedule. Since we're describing a home network that will connect to the Internet, you're strongly advised to install a protective firewall program to thwart Internet viruses, worms, or other damaging spyware code. Minimize, Restore, and Exit buttons - these three buttons are usually located on the right-most upper part of a program's interface and each allow you to minimize a program's screen, restore it to its original size, or shut down the program completely. Scroll bar - this convenient tool allows users to move data up and down the computer screen. In recent news, LiveScience.com reported that "Before the month is even done, April has set a record for virus e-mails."1 In the past, we would be comfortable in telling new computer users not to worry about viruses and that catching a computer virus is rare. Today, that would be some of the worst advice we could give anyone. And this is what puts open source projects far ahead of its monetized competition. As a software user, this means you can contribute to an open source project as well, and help to develop it into a product that reflects your direct preferences. You aren't "stuck" using open source software the way you would be stuck using an expensive word processor or database.