Virus - definition:
A computer virus is a malware program that, when executed, replicates by inserting copies of itself (possibly modified) into other computer programs, data files, or the boot sector of the hard drive; when this replication succeeds, the affected areas are then said to be "infected".1234 Viruses often perform some type of harmful activity on infected hosts, such as stealing hard disk space or CPU time, accessing private information, corrupting data, displaying political or humorous messages on the user's screen, spamming their contacts, logging their keystrokes, or even rendering the computer useless. However, not all viruses carry a destructive payload or attempt to hide themselves?the defining characteristic of viruses is that they are self-replicating computer programs which install themselves without user consent.
Virus writers use social engineering and exploit detailed knowledge of security vulnerabilities to gain access to their hosts' computing resources. The vast majority of viruses target systems running Microsoft Windows,567 employing a variety of mechanisms to infect new hosts,8 and often using complex anti-detection/stealth strategies to evade antivirus software.9101112 Motives for creating viruses can include seeking profit, desire to send a political message, personal amusement, to demonstrate that a vulnerability exists in software, for sabotage and denial of service, or simply because they wish to explore artificial life and evolutionary algorithms.13
Computer viruses currently cause billions of dollars' worth of economic damage each year,14 due to causing system failure, wasting computer resources, corrupting data, increasing maintenance costs, etc. In response, free, open-source antivirus tools have been developed, and an industry of antivirus software has cropped up, selling or freely distributing virus protection to users of various operating systems.15 Even though no currently existing antivirus software is able to uncover all computer viruses (especially new ones), computer security researchers are actively searching for new ways to enable antivirus solutions to more effectively detect emerging viruses, before they have already become widely distributed.16
A personal computer is a general-purpose computer whose size, capabilities and original sale price make it useful for individuals, and is intended to be operated directly by an end-user with no intervening computer time-sharing models that allowed larger, more expensive minicomputer and mainframe systems to be used by many people, usually at the same time.
Software applications for most personal computers include, but are not limited to, word processing, spreadsheets, databases, web browsers and e-mail clients, digital media playback, games and many personal productivity and special-purpose software applications. Modern personal computers often have connections to the Internet, allowing access to the World Wide Web and a wide range of other resources. Personal computers may be connected to a local area network (LAN), either by a cable or a wireless connection. A personal computer may be a laptop computer or a desktop computer running an operating system such as Windows, Linux (and the various operating systems based on it), or Macintosh OS.
Early computer owners usually had to write their own programs to do anything useful with the machines, which even did not include an operating system. The very earliest microcomputers, equipped with a front panel, required hand-loading of a bootstrap program to load programs from external storage (paper tape, cassettes, or eventually diskettes). Before very long, automatic booting from permanent read-only memory became universal. Today's users have access to a wide range of commercial software, freeware and free and open-source software, which are provided in ready-to-run or ready-to-compile form. Software for personal computers, such as applications and video games, are typically developed and distributed independently from the hardware or OS manufacturers, whereas software for many mobile phones and other portable systems is approved and distributed through a centralized online store.12
Since the early 1990s, Microsoft operating systems and Intel hardware have dominated much of the personal computer market, first with MS-DOS and then with Windows. Popular alternatives to Microsoft's Windows operating systems include Apple's OS X and free open-source Unix-like operating systems such as Linux and BSD. AMD provides the major alternative to Intel's processors.
You should keep your computer safe. What do You really know about viruses? If You think they are not dangerous, you are in a big mistake. In fact, computer virus can destroy all your data, but damage could be worse. What can you do when your computer gets infected? First try to use an antivirus program to scan your disk, it is still possible to remove a problem. What if it will not work?
In the worst case, call for help to a computer service - they will know what to do to fix your computer and save your files.