Smartphones are mobile phones with computer like capabilities. What's that? Aha! Yes, you've not only heard of them, you've probably seen them as well. Packed with Internet access, email capabilities, address books, and a whole lot more, cell phones have come a long way since their first debut. But be careful not to confuse these newest toys with sandbox devices. Other times, the data is unknown. If the program were working with a simple algebra equation like, "x + 5 = y," the variables "x" and "y" would be unknown pieces of data. Or if a program were to calculate a date "x" days from now, the variable "x" would be an unknown piece of data until we tell the program what "x" is. Some of the most common parts of a menu bar grants access to File commands, Open commands, Save commands, and Print commands. An example of an error in this part of an interface would be if an option was missing or grayed out (lighter in color). Tool bar - this part of a program displays small icons across the top which represent tools. Microsoft provides a section on its website that can automatically update a computer online and it does this at no cost in an effort to reduce errors like this. Always try to keep your computer updated so that should a program share a file, it will share a file that has been updated on hundreds of thousands of computers, like yours. 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. It attacks computers via distribution - often unknowingly - through email attachments, software downloads, and even some types of advanced web scripting. Viruses that destroy data are known as Trojan horses, viruses that explode their attacks are called bombs, and viruses that duplicate themselves are called worms.