Optionally, enter a password hint.

Part III ✦ Working with Networked Computers Using Mac network commands Each operating system for the Mac has distinctive networking commands and features. You should use these commands or applications only if you’re comfortable with the computer and you understand the consequences of your actions. Earlier versions of the Mac operating system, such as System 8 or 9, have a Network Assistant that you can use to help manage the network. Do not try to use the Network Assistant with Mac OS X, however; you could damage the operating system. Following are just a few of the incidents that could happen: The computer doesn’t start, the computer starts up with a flash- ing question mark, or a kernel panic happens during or after startup. Using Linux network commands Most distributions of Linux include network commands you can install. Common commands enable you to configure the network interface, display configuration, map drives, share print- ers, and so on. IFCONFIG is a command you can use to display the current configuration. It describes the IP address, subnet mask, and a broadcast address of the subnet. You can also use the PING com- mand with Linux boxes. NSTAT and NETSTAT are two commands that result in network statis- tics relating to the computer on which it is typed. Protecting the Network from Viruses One of the first procedures any computer should perform when it boots is to check for viruses. Viruses are computer programs that disrupt or destroy your files, file system, soft- ware, hardware, your work, or even your network. A virus might only display a message, or it could erase or reformat your hard disk. A virus can attack one computer and then travel the network to other computers and your server. New viruses are found daily, each with its own brand of destruction and aggravation. Your computer can catch a virus from a contaminated floppy disk, a file on the network, a file downloaded from the Internet, or a file attached to an e-mail message; a virus can even ride on the back of a worm through your Internet connection. After it’s infected, your computer crashes and burns; worse yet, your infected computer could take down the entire network. Your network is only as strong as its weakest computer when it comes to fighting viruses and worms. Because viruses can quickly spread over the network, it’s important that all computers on the network are protected. Many computers come with an antivirus program installed — Symantec or Norton AntiVirus or McAfee VirusScan, depending on the computer manufacturer. Many other antivirus applications are available. You should use a virus program daily, and you should keep the program’s list of viruses called definitions and cures updated. Discuss with your employees the danger of bringing disks from home and downloading files from the Internet — especially e-mail. Also, require all users to keep an antivirus program run- ning on their computers all the time so that it catches viruses as they appear on the com- puter. One virus spread to a network can cost hundreds of thousands of dollars in hardware damage and data corruption. Small Business Tip Note Chapter 13 ✦ Accessing the Network You can set the properties on most antivirus programs. In most cases, you can tell the pro- gram to load when you boot the computer and then scan files of various types. You also tell the program how to react to finding a virus — whether to alert you or the entire network, quarantine or delete the infected file, and so on. You also must be careful with antivirus programs. Some programs can cause problems with computer or networking hardware, operating systems, and even other programs on the com- puter. To help guard against problems, buy only reputable brand name antivirus programs. Free antivirus programs are not usually worth the time it takes to download them. If your computer, network, or programs have problems, disable the antivirus program and see if that helps alleviate your trouble. You also might check the Internet for reported problems. Looking closer at viruses Computer viruses infect other programs by copying themselves into the program. They also try to hide within the program by encrypting themselves. Many viruses mutate slightly every time they replicate, so as to escape detection. Viruses can even mutate and replicate from computer to computer on a private network. You have to watch out for all sorts of attacks: viruses, worms, Trojan horses, and even hoaxes. If you have a question about a virus or you need to fix a virus your antivirus program missed, check the Symantec site: www.sarc.com. Nuisances and viruses One of the worst viruses to date is Klez with variations called W32.Klez.Hmm, Klez A, Klez D, Klez E, Klez H, and anything with Klez in the name. This virus is a mass-mailing e-mail worm. Klez is difficult to remove once it gets a hold of your computer. Klez fills the hard drive with trash and garbage while destroying data and overwriting files. Then, it travels across your network easily and efficiently. If you discover a virus on any computer connected to your network, the first thing to do is unplug the cable from the network so the virus cannot travel to other computers. If you’re using a wireless network, turn the infected computer off until you can verify the safety of the other computers. Unplug the access point near the infected computer before turning it back on to apply a fix. Some viruses do more than make copies of themselves: They issue instructions that disrupt the computer’s normal processes. Viruses often use the computer’s clock to trigger the disruption — from displaying a message to crashing a hard disk. The Michelangelo virus is one of those that activates according to the clock: Yearly, on March 6, Michelangelo’s birth- day, the virus takes over your hard disk. There are other types of nuisances, and not all are classified as viruses: ✦ The Melissa virus, for example, is actually a Microsoft Word macro. Macros are mini- programs that run when a file is opened or you actually initiate the macro. Many pro- grams use macros — Word and WordPerfect, for example — and even let you create macros that can make your work easier and help you complete tasks more quickly. However, there are macros that can activate within a program and destroy your docu- ments. Melissa travels in a Word document and is activated only when the document is opened in Word. If you don’t open the document containing the macro, the macro isn’t activated. Melissa is contained in a file attached to e-mail messages. Tip Note