Viruses
A virus in nature is a tiny organism that literally hovers at the edge of the living and the non-living. If it infects a host, it comes alive, using the host's resources to rapidly make many copies of itself, while possibly causing harm to the host. (There are some viruses that do no harm, or which might even benefit the host, living in a symbiotic relationship.) If it is not in a host and is left by itself, it is completely inert, consuming no resources and performing no actions indicative of life. In much the same way, a computer virus is a software program that is capable of infecting a host machine, and then making copies of itself while doing harm to the host.
Computer viruses have to be executable program code, and cannot be inert files that do not cause the computer to act. There are several common kinds of viruses: some can infect the "boot sector" of floppy disks or hard drives; others are called macro viruses because they infect other software that uses macros. Some viruses are spread as attachments to e-mail, while others are spread by sharing infected floppy disks and other media.
When a user tries to execute a program that has been infected, the virus is made active and becomes resident in the computer's primary storage or random-access memory (RAM). While the virus is active in the computer's RAM, any other program that is run will also become infected. If the computer is then shut off, re-starting it and invoking an infected program would cause the virus to become active again. If an infected program is used to write to a floppy disk or other medium, then the file written to is also infected, and will infect other computers if read on them. For this reason, it is commonly advised to do a "virus scan" on all unknown disks and other media before loading them on one's computer. A virus that is spread by e-mail is released when an attachment containing the virus's executable code is opened. The virus then causes a certain e-mail message to be sent to all the addresses stored in a user's online address book, and also does harm to the user's own machine. Persons who receive the infected e-mail from the user are safe if they do not open the attachment they receive. However, it is not uncommon for people to see a message from someone they know well and think the attachment must not be harmful, thus propagating the destructive chain further.
A computer virus has to have been created by deliberate effort; it doesn't arise by accident or just happen to be. Since computer viruses can severely damage software and data resulting in loss of information and much work for repair and restoration, they are threats to computer system security, and are thus taken seriously. In the United States, it is a felony under Federal law to create a virus that does serious damage to computer systems, and serious fines or imprisonment may result.
Unfortunately, a great many myths and hoaxes exist on the subject of computer viruses. It is not uncommon to find chain e-mail claiming to warn of some impending disaster due to a very severe virus outbreak. Some people even think that the harm caused in terms of lost productivity and such by virus hoaxes is even greater than that caused by real viruses. In this regard, we should note some common fallacies about viruses. Viruses are specific to certain operating systems, i.e., it is not possible for a virus to infect both a Windows machine and a UNIX machine, for example. Viruses also do not directly harm software, so if there is a "virus warning" about an online pathogen that would make one's computer explode, one knows it is false. One cannot also catch a virus simply by reading e-mail or performing other common, everyday tasks.
To reduce the chances of being exposed to and affected by viruses, everyone should adopt certain habits of safety. These include not opening any strange or unexpected attachments that show up in one's e-mail. If one is not sure why someone known to oneself is sending a certain message with an attachment, it is better to check with the sender whether the attachment was really purposeful. Reading the message itself is not risky, but opening the attachment might be. Another good measure is to avoid sharing files and programs without running a "virus scan" on them. In fact, there are specialized "anti-virus" software programs that detect and remove many common viruses. Since viruses are created on an ongoing basis, it is necessary for one to be using the latest version of the anti-virus software in order to obtain the best possible protection. In order to obtain safety it is also a good idea to back up one's computer files on a regular basis. In case the files are lost due to a virus infection, or even due to any other cause, one would then be able to go to retrieve them from storage.
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