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What is a computer virus?

What is a computer virus?



Definition:- 

A computer virus is a malicious software program loaded onto a user’s computer without the user’s knowledge and performs malicious actions.
A computer virus, much like a flu virus, is designed to spread from host to host and has the ability to replicate itself.
 Similarly, in the same way, that flu viruses cannot reproduce without a host cell, computer viruses cannot reproduce and spread without programmings such as a file or document.

In more technical terms, a computer virus is a type of malicious code or program written to alter the way a computer operates and is designed to spread from one computer to another.
 A virus operates by inserting or attaching itself to a legitimate program or document that supports macros in order to execute its code.
 In the process, a virus has the potential to cause unexpected or damaging effects, such as harming the system software by corrupting or destroying data.
Description: The term 'computer virus' was first formally defined by Fred Cohen in 1983. Computer viruses never occur naturally.
 They are always induced by people. Once created and released, however, their diffusion is not directly
under human control.
 After entering a computer, a virus attaches itself to another program in such a way that the execution of the host program triggers the action of the virus simultaneously.
 It can self-replicate, inserting itself onto other programs or files, infecting them in the process. Not all computer viruses are destructive though.
 However, most of them perform actions that are malicious in nature, such as destroying data. Some viruses wreak havoc as soon as their code is executed,
 while others lie dormant until a particular event (as programmed) gets initiated, which causes their code to run on the computer.
 Viruses spread when the software or documents they get attached to are transferred from one computer to another using a network, a disk, file sharing methods, or through infected e-mail attachments.
 Some viruses use different stealth strategies to avoid their detection from anti-virus software. For example, some can infect files without increasing their sizes, while others try to evade detection by killing the tasks associated with the antivirus software before they can be detected.
 Some old viruses make sure that the "last modified" date of a host file stays the sam


The common type of computer viruses here,

Boot Sector Virus
Direct Action Virus
Resident Virus
Multipartite Virus
Polymorphic Virus
Overwrite Virus
Spacefiller Virus

Boot Sector Virus This type of virus infects the master boot record and it is challenging and a complex task to remove this virus and often requires the system to be formatted. Mostly it spreads through removable media.

Direct Action VirusThis is also called a non-resident virus, it gets installed or stays hidden in the computer memory. It stays attached to the specific type of files that it infects. It does not affect the user experience and system’s performance.

Resident Virus Unlike direct action viruses, resident viruses get installed on the computer. It is difficult to identify the virus and it is even difficult to remove a resident virus.

Multipartite VirusThis type of virus spreads through multiple ways. It infects both the boot sector and executable files at the same time.

Polymorphic Virus – These types of viruses are difficult to identify with a traditional anti-virus program. This is because the polymorphic viruses alter its signature pattern whenever it replicates.

Overwrite Virus This type of virus deletes all the files that it infects. The only possible mechanism to remove is to delete the infected files and the end-user has to lose all the contents in it. Identifying the overwrite virus is difficult as it spreads through emails.

Spacefiller Virus This is also called “Cavity Viruses”. This is called so as they fill up the empty spaces between the code and hence do not cause any damage to the file.

File infectors: Few file infector viruses come attached with program files, such as .com or .exe files. Some file infector viruses infect any program for which execution is requested, including .sys, .ovl, .prg, and .mnu files. Consequently, when a particular program is loaded, the virus is also loaded.

Macro viruses: As the name suggests, the macro viruses particularly target macro language commands in applications like Microsoft Word. The same is implied in other programs too.In MS Word, the macros are keystrokes that are embedded in the documents or saved sequences for commands. The macro viruses are designed to add their malicious code to the genuine macro sequences in a Word file. However, as the years went by, Microsoft Word witnessed disabling of macros by default in more recent versions. Thus, the cybercriminals started to use social engineering schemes to target users. In the process, they trick the user and enable macros to launch the virus.

Do’s

Use a professional, email service such as Runbox. Subscription services provide higher levels of security and support.
Make sure that your Runbox virus filter is activated.
Use the Webmail interface at www.runbox.com to read your email, or don’t download all your email to an email client unseen. Screen your email first, and delete suspicious-looking and unwanted messages before downloading the legitimate email to your local email client.
Make sure your computer has updated anti-virus software running locally. Automatic updates are essential for effective virus protection. Combined with server-side scanning, you now have two layers of security.
Disable message preview in your email client, especially on Windows platforms.

And the main mandatary is Latest Antivirus available to your system, don't use without antivirus 




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