Malware

What is a computer virus?


Authored by a Symantec employee

 

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 programming 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.

How does a computer virus attack?

Once a virus has successfully attached to a program, file, or document, the virus will lie dormant until circumstances cause the computer or device to execute its code. In order for a virus to infect your computer, you have to run the infected program, which in turn causes the virus code to be executed.

This means that a virus can remain dormant on your computer, without showing major signs or symptoms. However, once the virus infects your computer, the virus can infect other computers on the same network. Stealing passwords or data, logging keystrokes, corrupting files, spamming your email contacts, and even taking over your machine are just some of the devastating and irritating things a virus can do.

While some viruses can be playful in intent and effect, others can have profound and damaging effects. This includes erasing data or causing permanent damage to your hard disk. Worse yet, some viruses are designed with financial gains in mind.

How do computer viruses spread?

In a constantly connected world, you can contract a computer virus in many ways, some more obvious than others. Viruses can be spread through email and text message attachments, Internet file downloads, and social media scam links. Your mobile devices and smartphones can become infected with mobile viruses through shady app downloads. Viruses can hide disguised as attachments of socially shareable content such as funny images, greeting cards, or audio and video files.

To avoid contact with a virus, it’s important to exercise caution when surfing the web, downloading files, and opening links or attachments. To help stay safe, never download text or email attachments that you’re not expecting, or files from websites you don’t trust.

What are the signs of a computer virus?

A computer virus attack can produce a variety of symptoms. Here are some of them:

  • Frequent pop-up windows. Pop-ups might encourage you to visit unusual sites. Or they might prod you to download antivirus or other software programs.
  • Changes to your homepage. Your usual homepage may change to another website, for instance. Plus, you may be unable to reset it.
  • Mass emails being sent from your email account. A criminal may take control of your account or send emails in your name from another infected computer.
  • Frequent crashes. A virus can inflict major damage on your hard drive. This may cause your device to freeze or crash. It may also prevent your device from coming back on.
  • Unusually slow computer performance. A sudden change of processing speed could signal that your computer has a virus.
  • Unknown programs that start up when you turn on your computer. You may become aware of the unfamiliar program when you start your computer. Or you might notice it by checking your computer’s list of active applications.
  • Unusual activities like password changes. This could prevent you from logging into your computer.

How to help protect against computer viruses?

How can you help protect your devices against computer viruses? Here are some of the things you can do to help keep your computer safe.
 
  • Use a trusted antivirus product, such as Norton AntiVirus Basic, and keep it updated with the latest virus definitions. Norton Security Premium offers additional protection for even more devices, plus backup.
  • Avoid clicking on any pop-up advertisements.
  • Always scan your email attachments before opening them.
  • Always scan the files that you download using file sharing programs.

What are the different types of computer viruses?

    1. Boot sector virus

    This type of virus can take control when you start — or boot — your computer. One way it can spread is by plugging an infected USB drive into your computer.

    2. Web scripting virus

    This type of virus exploits the code of web browsers and web pages. If you access such a web page, the virus can infect your computer.

    3. Browser hijacker

    This type of virus “hijacks” certain web browser functions, and you may be automatically directed to an unintended website.

    4. Resident virus

    This is a general term for any virus that inserts itself in a computer system’s memory. A resident virus can execute anytime when an operating system loads.

    5. Direct action virus

    This type of virus comes into action when you execute a file containing a virus. Otherwise, it remains dormant.

    6. Polymorphic virus

    A polymorphic virus changes its code each time an infected file is executed. It does this to evade antivirus programs.

    7. File infector virus

    This common virus inserts malicious code into executable files — files used to perform certain functions or operations on a system.

    8. Multipartite virus

    This kind of virus infects and spreads in multiple ways. It can infect both program files and system sectors.

    9. Macro virus

    Macro viruses are written in the same macro language used for software applications. Such viruses spread when you open an infected document, often through email attachments.

How to remove computer viruses

You can take two approaches to removing a computer virus. One is the manual do-it-yourself approach. The other is by enlisting the help of a reputable antivirus program.

Want to do it yourself? There can be a lot of variables when it comes to removing a computer virus. This process usually begins by doing a web search. You may be asked to perform a long list of steps. You’ll need time and probably some expertise to complete the process.

If you prefer a simpler approach, you can usually remove a computer virus by using an antivirus software program. For instance, Norton AntiVirus Basic can remove many infections that are on your computer. The product can also help protect you from future threats.

Separately, Norton also offers a free, three-step virus clean-up plan. Here’s how it works.

  1. Run a free Norton Security Scan to check for viruses and malware on your devices. Note: It does not run on Mac OS.
  2. Use Norton Power Eraser’s free virus and malware removal tool to destroy existing viruses. Need help? A Norton tech can assist by remotely accessing your computer to track down and eliminate most viruses.
  3. Install up-to-date security software to help prevent future malware and virus threats.

Our best protection. One low price

Norton Security Premium helps protect up to 10 of your Windows PCs, Macs, Android smartphones or your iPads.


Symantec Corporation, the world’s leading cyber security company, allows organizations, governments, and people to secure their most important data wherever it lives. More than 50 million people and families rely on Symantec’s Norton and LifeLock comprehensive digital safety platform to help protect their personal information, devices, home networks, and identities.

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