The term, ?virus?, in computer technology, refers to a self replicating application that spreads by making copies of itself by inserting into other programs, other executables or documents, and when executed begins to perform harmful actions on the system. All computer viruses are deliberately created, not always malicious and some of them may be benign and simply annoying.
Non-Memory Resident and Memory Resident Viruses:
Non-Memory resident viruses, when they are executed, immediately look for other hosts that can be infected. When they infect these targets, they transfer control to the application program they infected. A non-resident virus has a finder module and a replication module. The finder module, once it finds a new file to infect, calls upon the replication module to infect that file.
Memory-Resident virus stays in the memory and do not look for hosts to infect when they are executed. It stays active in the background after its host program is terminated, and infects files as soon as they are opened or accessed by other programs or the operating system. It does have the replication module like the non-memory resident virus, but without the finder module.
Types of Computer Viruses:
File Viruses: These types of viruses are the most common, and mostly infect open files and program libraries on an operating system. The virus functions by inserting itself into a host file, modifies it in such a way that the virus is executed when the file is opened. They are also known as left viruses. Today, there are known viruses infecting all kinds of executables of standard DOS: batch command files (BAT), loadable drivers (SYS, including special purpose files IO.SYS and MS- DOS.SYS) and binary executables (EXE, COM). There are also viruses targeting executables of other operating systems - Windows 3.x, Windows95/NT, OS/2, Macintosh, Unix, including the VxD drivers of Windows 3.x and Windows95.
Macro viruses: Macros are used in most word processing programs such as Microsoft Office in order to automate or simplify recurring tasks in documents. Macro viruses are those viruses that use the application's own macro programming language to distribute themselves, in which an unwanted sequence of actions is performed automatically when the application is started or something else triggers it. These macro viruses may inflict damage to the document or to other computer software but are relatively harmless, and are often spread as an e-mail virus.
Boot Viruses: These were one of the most common viruses prevalent during the early and mid 1990s, when the use of diskettes was popular. These viruses infect or substitute their own code for either the DOS boot sector or the Master Boot Record (MBR), which controls the boot sequence of the PC. The MBR is executed every time a computer is booted so the virus will also be loaded into memory on every startup and spreads to every disk that the system reads. They are typically very difficult to remove, and most antivirus programs cannot clean the MBR while Windows is running. So, bootable antivirus disks are needed to fix boot sector viruses.
Effects Of Computer Viruses
What are computer viruses? Many computer users would find it hard to answer that question. In fact the definition of a virus has nothing to do with what terrible damage it may inflict on your computer. It is just a question of how it spreads. A virus is a program (usually a file ending in .exe) that has the ability to clone itself and transmit its clones to other computers. This system of 'infection', resembling the spread of viral diseases, is why it is called a virus.
Of course, unlike viral diseases, computer viruses are not carried by insects or spread by coughs and sneezes. Instead, their carriers are digital. Your computer may be infected with a virus by a data disk or CD that you insert, a file that you download from the internet, or an email. It is even possible to download a virus by simply visiting a web page and then clicking away.
What a virus does when it reaches your computer depends on what it is programmed to do. If it is an email-borne virus then the first thing it will do will be to try to spread itself on to your contacts, usually by sending out an email to everyone in your address book. Then it will go ahead and fulfill its primary purpose. This can be almost anything from displaying a message on your screen through corrupting your files and even wiping your hard drive clean, destroying all your data.
Most viruses are developed by people of a destructive mindset either for their own sadistic amusement or to show their friends how clever they are. Occasionally they have a different purpose such as collecting your personal data and relaying it to their creator for ID theft or hacking into your systems. This could cost you even more than the loss of your stored data. Even if a virus is not destructive it is usually annoying, repeatedly displaying messages on your screen or making your computer less efficient and slower.
Most viruses can be detected and removed if you have good anti virus software. With new viruses being developed and released almost daily, it is important to keep your anti virus program updated, otherwise you may not know that you have a virus until it is too late. But even if you scan your system regularly, a fast-acting virus may have already inflicted some damage. Just as with human diseases, prevention is better than cure.
Both George Royal & Kerry Graylor are contributors for EditorialToday. The above articles have been edited for relevancy and timeliness. All write-ups, reviews, tips and guides published by EditorialToday.com and its partners or affiliates are for informational purposes only. They should not be used for any legal or any other type of advice. We do not endorse any author, contributor, writer or article posted by our team.
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