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What is Virus?



A computer virus is a computer program copy itself and infects a computer without permission or knowledge of the user. The term computer virus program which has infected some executable software and which causes that software, when run, to spread the virus to other executable software. A computer virus is a program that infects the computer and it creates duplicate without permission or knowledge of the user. It is like a metamorphic virus, that it may modify the copies, or the copies may modify themselves.

A virus can only spread from one computer to another, by instance a user sending a data over a network or the Internet, or by carrying it on a removable medium such as a floppy disk, CD or USB Drive.


An alternative terminology in which a virus is any form of self-replicating  is called Malware.  It is  also known as Malicious Software, designed to infiltrate or damage a computer system without the owner's informed consent.

Adware or advertising-supported software is any software package which automatically plays, displays, or downloads advertisements to a computer after the software is installed on it or while the application is being used. Some types of adware are also Spyware and can be classified as privacy-invasive software. Some adware is also shareware. Some programs are designed specifically for spyware detection and will not detect viruses, although some commercial antivirus software can also detect adware and spyware, or offer a separate spyware detection package.

Computer worms

Trojan Horses

Trojan horse is a file that appears harmless. Today's viruses may also take advantage of network services that given below, systems to spread, blurring the line between viruses and worms.

  • World Wide Web
  • E-mail
  • Instant Messaging
  • File Sharing
Types of Trojan horse payloads

Trojan horse payloads are almost always designed to cause harm, but can also be harmless. They are classified based on how they breach and damage systems. The six main types of Trojan horse payloads are:

  • Remote Access
  • Data Destruction
  • Down loader
  • Server Trojan(Proxy, FTP , IRC, Email, HTTP/HTTPS, etc.)
  • Security software disabler
  • Denial-of-service (Dos)

Some examples of damage are

  • Erasing or overwriting data on a computer
  • Re-installing itself after being disabled
  • Allowing remote access to the victim's computer. This is called a [ RAT Remote access Trojan ]
  • Phishing for bank or other account details, which can be used for criminal activities
  • Copying fake links, which lead to false websites, chats, or other account based websites, showing any local account name on the computer falsely engaging in untrue context
  • Restarting the computer whenever the infected program is started
  • Randomly shutting off the computer

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