A computer virus is a program, which arbitrarily joins to other computer programs and during their action performs a variety of undesired actions: damages data, catalogues, computational results, deletes or pollutes a memory, and interferes computer’s performance in many other ways. Computer viruses usually multiply themselves by infecting disc data or system areas. If there is no anti-virus software in the computer, you can detect virus only then, when they have started an active performance.
A computer virus is a program, which spreads from one computer to other and interferes their performance. Computer viruses are often spread with attachments of e-mails, therefore never open an attachment if you do not know the sender or you do not wait for any attachment. Viruses may be hidden like attachments as funny pictures, greeting cards, audio files, or video files. Viruses also spread, downloading different files from the Internet – they may be hidden in some piracy software or in other files or programs, which you are downloading.
Computer viruses act similarly as biological viruses – they can be in the computer for long time without any evidence. Different viruses are activated differently, for example, there is a virus, which usually is activated, when 13th date falls on Friday. Also their expressions are different – there are viruses, which are pretty harmless, but there are also viruses, which can destroy all the data.
Signs, which distinguish viruses from programs:
- Viruses are activated without user’s permission and are performing actions of programmer, not user;
- They have ability to infect or change files or structure of discs;
- By multiplying themselves they can spread to other files and systems;
- Viruses are made by using the same programming languages, which are made by macros of such applications as Assembler, C, Visual Basic, Java, and others.
What is a Worm?
A worm is a computer code, which spreads without user’s knowledge. Worms are usually obtained with e-mail attachments – when they are opened, the computer is infected. Worms search for files, which contain e-mail addresses, for example, address books or temporary sites. Worms use these addresses to send infected e-mail messages and often imitate addresses of e-mail senders (pretending to be other sender), therefore it often seems that infected messages are known person’s messages. Then worms spread, using vulnerability of e-mail messages, networks, or operating systems, often taking over the system before the cause of problem is known. Worms not only harm computers, but also cause operational and stability problems of computer and network.
What is a Trojan Horse?
A Trojan horse is a malicious program, which hides in other programs. It gets in the computer, hiding in some legal program, for example, in some screensaver. Then it enters the code of operational system, providing hackers an access to the infected computer. Trojan horses usually do not spread themselves – they are spread by computer viruses, worms and downloaded software.