Copyright Goodheart-Willcox Co., Inc. 450 Networking Fundamentals to gain access to a network, an unauthorized person may try to use what they think is a valid IP address to fool a server. Another example is to use a fake IP address and ID when sending an unsolicited e-mail to someone. Th e e-mail can be used to solicit information or release a worm. It is a good policy never to respond to an unsolicited e-mail. A common ploy is to send unsolicited e-mails to millions of possible legitimate e-mail addresses using a software program that generates possible e-mail addresses. In the e-mail, a line is included that states: “If this e-mail was sent by mistake and you wish to be removed from our e-mail list, please click the link below.” Th e link is intended to generate a list of everyone who replies. Th e list is valuable because it contains a list of real e-mail addresses that can be sold or distributed to interested parties, such as advertisers. By responding to the removal link, you are actually verifying the e-mail address used was a genuine e-mail address. Malware Malware, short for malicious software, is a term given to software programs that are intended to damage, destroy, or steal data. Often, malware is disguised as something innocent but has devastating eff ects. For example, clicking an unsolicited link in an e-mail can trigger a line of code that will leave a computer or network vulnerable to infection. Malware comes in many forms including Trojan horses, viruses, worms, ransomware, and logic bombs. Trojan Horse A Trojan horse is a program designed to gain access to a computer while pretending to be something else. For example, a user downloads what he or she thinks is a free game. A real game may indeed be inside the download, and for a good Trojan horse design, it should be. However, in addition to the game program code is code of a ma- licious nature. Th e malicious code could contain a virus, worm, or what is known as a backdoor. A backdoor is a software access port to a computer infected by a Trojan horse. Another common purpose for a Trojan horse is to download a program that imitates the logon screen of a legitimate operating system. When the user logs on using the Trojan horse fake logon screen, the user’s name and password is sent to an unauthorized user for later use in gaining access to the computer. Virus A virus is software that self-replicates. Th ere are many diff erent types of viruses, and some of the major categories will be discussed in this section. It is important to note that modern malware often combines elements of diff erent categories. For example, a given malware infection could be a virus that also delivers a Trojan horse, and the Trojan horse then contains software to launch a DDoS attack. Macro Virus One of the most common and most easily written virus programs is a macro virus. Many legitimate software programs, such as word-processing packages, contain a special tool called a macro writer. Th e macro writer records and saves certain key- stroke sequences as a convenience for the user. For example, a user can make a mac- ro that inserts his or her return address into a document when he or she pressees a specifi c key sequence. Th e macro program is handy for reducing the amount of work involved for repetitive tasks. Th e same principle can be used to create viruses. A series of commonly used keystrokes can be linked to a virus. Th e macro is sent as an e-mail attachment and is launched when the e-mail recipient opens the attachment. Tech Tip The terms malware, virus, and worm are often used inter- changeably even though this is not technically correct.