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Junk E-Mail or Spam:
Many computer users also see junk e-mail as another form of privacy invasion. When your e- mail inbox is filled with unwanted message, you must spend time and energy reviewing and removing these unwanted messages. This process means lost productivity for many individuals and businesses.
Junk e- mail- better known as spam, and also as unsolicited commercial e- mail (UCE)- is a lot like old-fashioned junk mail; that is, you open your e- mail program’s inbox and find unwanted messages from various senders. Like traditional junk mail, spam usually includes solicitations to buy something, or invitations to participate in get-rich-quick schemes. Some junk e-mail messages, however, are filled with obscene material.
The two most popular trick user by junk e-mailers are spamming and spoofing. In spamming, the sender (called a spammer) sends hundreds, thousands or even then of thousands of messages to recipients across a wide geographical.
Spammers are very creative when it comes to getting the e-mail addresses of their recipients. Some rely on mailing lists purchased or hacked from the databases of legitimate marketers or service providers. Others simply use programs that generate addresses randomly based on the domain names of known Internet service providers (ISPs).
A more difficult technique, called spooning, enables the junk e-mailer to hide his or her identity from the recipient. In spoofing, the senders place a false return address on the junk message. When spoofing, the recipient has no idea who sent the message and has no way or responding or stopping the problem.
There are other types spoofing on the Internet too. One type, called Web spoofing, is a technique for hijacking legitimate Web pages and using them to route visitors to another side.

Software Piracy: 
The biggest legal issue affecting the computer industry is software piracy, which is the illegal copying of computers programs and operating systems. Software pirates give up the right to receive upgrades and technical support, but they gain the use of the program without paying for it.

How pirates work:
 Software is pirated in many ways. The simplest method is to copy the software from its original floppy disk or compact disk. Users on a network can copy certain types of software directly from the server or even exchange programs over their organization’s e-mail system. Determined, sophisticated pirates can crack a programs built-in registration or copy protection system, an ability that has earned the nickname “crackers”.
The Internet has become the biggest hotbed of piracy because pirates distribute programs by e-mail, across World Wide Web sides, on FTP servers, in newsgroups and through chat rooms. Certain Web sides and newsgroups-have become notorious for posting entire operation systems, upgrades, and commercial applications for anyone to download and commercial applications for anyone to download and use.

Although hardware theft has been going on many years, the problem was not particularly seriously until the introduction of PCs made valuable equipment much easier to move. The problem has skyrocketed with the popularity of small portable computers. Many organizations now secure their computer equipment with steel cables.
Hackers are experts in computer technology who take great pleasure in solving software problems, frequently by circumventing established rules or security system. Often, these experts are tempted by the power of their skills and become criminals. They can steal data, transfer money from one account to another, or crash computer systems.

Computer Viruses:
A virus is a parasitic program that infects another legitimate program, which is sometimes called the host. To infect the host program, the virus modifies the host to store a copy of the virus. Many viruses are programmed to do harm once they infect the victim’s system. But the ability to do damage is not what defines a virus. To qualify as a virus, a program must be able to replicate (make copies of itself). This can mean copying itself to different places on the some computer or looking for ways to reach other computers, such as by infecting disks or traveling cross networks.

Categories of Viruses:
1.     Boot Sector Viruses:  Regarded as one of the most hostile types of virus, a boot sector virus infects the boot record of a hard or floppy desk.
2.     Cluster viruses: This type of virus cakes changes to a disk’s file system.
3.     File-Infecting Viruses: This type of virus infects program file on a disk. When an infected program is launched. The virus code is also executed.
4.     Worms: A worm is a program whose purpose is to duplicate itself; an effective worm will fill entire desks with copied of itself.
5.     Bombs: This type of virus hides on the user’s disk and waits for a specific event to occur before running.
6.     Trojan Horses: A Trojan Horses is a malicious program that appears to be friendly. For example. Some Trojan Horses appear to be games. Because Trojan Horses do not make duplicates of themselves on the victim’s disk they are not technically viruses. But, because they can do harm, they are considered viruses.
7.     Polymorphic, Self-Garbling, Self-Encrypting or Self-Changing Viruses: This type of virus can change itself each time it is copied, making it difficult to isolate.
8.     Stealth Viruses: These viruses take up residence in the computer’s memory, making them hard to detect. They can also conceal changes they make to other files, hiding the damage from the user and the operating system.
9.     Micro Viruses: A macro virus is designed to infect a specific type of document file, such as Microsoft Word or Excel files. A micro virus is embedded in a document file and can do various levels of damage to data from corrupting documents to deleting data.
10.   Joke Programs: Joke programs are not viruses and do not inflict any damage. Their purpose is to frighten their victims into thinking that a virus has infected and damage their system.
11.   Bimodal, Bipartite, or Multipartite Viruses: this type of virus can infect both files and the boot record of a disk.

Viruses can be programmed to do many kinds of harms, including the following:
o   Copy themselves or other programs or areas of a disk.
o   Display information on the screen.
o   Destroy data files.
o   Erase the contents of an entire disk.
o   Lie dormant for a specified time or until a given condition is met and then become active.
o   Open a “back door” to computer, which allow someone else to access and event take control of the system via an Internet connection.

Preventing Infection:
Safeguarding a system against viruses is not difficult if you have a little knowledge and some utility software. Following are some common ways to pick up a virus.
o   Receiving an infected disk from another user. In this case, the virus could be in the boot sector of the disk or in an executable file on the disk.
o   Downloading an infected file to computer across a network, an online service, or the Internet.
o   Copying to your disk a document file that is infected with a macro virus. An infected document might be copied from another disk or received as an attachment to an e-mail message.