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What are the characteristics of a virus?
A computer virus is a programme designed to alter the way a computer operates, without the knowledge or consent of the user. There are two key aspects of a virus:
1 They are self executing. Typically, a virus will attach itself to another programme on your computer, so that it is activated when that programme is used
2 They are self-replicating. Viruses are designed to spread from machine to machine and across networks. To achieve this, a virus will usually copy itself to other programmes on a computer, before executing any intended tasks
There are a huge number of viruses in existence, carrying varying degrees of risk. Some are extremely malicious, with the ability to delete or damage files and programmes. Others are less destructive, but prove debilitating by jamming resources, causing systems to crash with consequent loss of data.
Some of the most well known viruses are:
Some viruses will hit as soon as they reach a machine, and signs of infection are immediately obvious. Others can remain hidden until triggered by a future event. It is therefore vital that full and thorough recovery procedures are followed when an infection occurs.
Although there is a large number of viruses, they fall into three main types:
You may also have seen the terms worm and trojan horses used in the context of viruses. These are variations on viruses with their own characteristics.
A worm is a programme that is designed to replicate and spread throughout a computer system. It will usually hide within files (for example, Word documents), and distribute those files through any available network connections.
Worms are often used to drain computer resources such as memory and network access, simply by replicating on a large scale. In addition, worms sometimes delete data and spread rapidly via e-mail.
A trojan horse is a malicious programme, usually disguised as something useful or desirable. When activated, they can cause loss, damage or even theft of data.
The critical difference between a trojan horse and a virus is that a trojan horse cannot replicate itself. The only way that a trojan horse can spread is if you help it! For example, saving the programme from an e-mail attachment, or downloading it from the Internet.
Just because trojan horse programmes are not self-replicating, it does mean that they are any less destructive than a virus. Some common features of trojan horse programmes include:
Some of the most common characteristics of a virus are:
See what are the signs of virus infection? for further advice on what to look for if you are concerned about a possible infection. Remember that just because you have some signs of a virus, it may not in fact be the case. It might be a virus hoax.
Viruses are usually disguised as something else. For example:
You are at risk from a computer virus infection if your computer system is used to communicate with others, be it via a network, the Internet or e-mail. Given that these are now the main reasons that we are using computers, the risks are very real.
There is a lot that you can do to protect your organisation against the threat of virus attacks. For further advice see our Virus Prevention and Good Housekeeping sections.
If you are concerned about your own risk from viruses, check the Virus Risk page, or run a Health Check now.
If you have suffered a virus attack, check the Virus Recovery page.