Below you will find the definition of many common terms:

What is Malware?
Malware is a general, catch-all name given to computer software that is designed to get onto a computer without the users permission and either damage a system (an individual application, functionality, or operating system), or send information, act as an annoyance.

The term itself is still not very popularly known, "computer virus" is usually used in its place. Viruses are only one form of malware, however. Other forms of malware include worms, trojans, spyware, adware and rootkits. These terms are explained below.

A lot of the time, malware may fall into more than one of these categories. For example, an adware may also be a spyware. As such, several types of removal tools may recognise the same infection. Different vendors may call them different names (though many keep standard names) so different tools recognising different infections may not necessarily mean that you have more than one infection.


What is a Virus?
A virus is the name given to one specific type of malware. A virus is designed to infect your computer files by making copies of itself in your system. It may spread from computer to computer if two computers are networked in such a way as one can read and write to the others files. Strictly speaking, viruses are unable to spread themselves to another computer by themselves without being transferred with a "host" infected file.

Viruses may designed to cause problems with your computer, send information to the designer, or interfere with day to day computing.


What is a Worm?
A worm is a program designed to use a computer network to send copies of itself to other computers, usually without the users knowledge or permission. While some worms have been designed to change settings or behavior on the infected computer, all worms are designed to cause issues for infected networks by spreading quickly from machine to machine and consuming available bandwidth.

More dangerous worms can also install software on a users computer (such as spam email servers), or change settings and manipulate data on your system.


What is a Trojan?
A Trojan Horse (or simply just trojan) is a form of malware that infects your computer by disguising itself as a harmless file. Once the file is opened or run on your computer, the trojan is able to infect the computer as intended.

Strictly speaking trojans don't copy themselves from computer to computer, they rely on manipulating the user into believing the file is harmless. However, other forms of malware may use trojans or trojan techniques to copy themselves from computer to computer, relying on the user to accept the file.


What is Spyware?
Spyware is software that installs itself on your computer without your permission and interfere with your actions on your computer. It can also be used to collect information about you, for example what websites you visit, or even financial information. Spyware can be used to change settings on your computer, redirect your web browsing, and install other software on your computer without your permission. It can be used to allow entry to other forms of malware to your computer.

Unlike viruses and worms, spyware does not usually self-replicate. Instead, it is usually installed on a computer by making the user think they are installing something else (acting as a trojan), or by exploiting a weakness in the operating system or an application. Sometimes spyware might even be included with a legitimate application installer.


What is Adware?
Adware is any software that displays or downloads advertisements while the software is in use. This may sometimes be a conscious decision on the part of the application developers in order to be able to generate revenue to continue development of the application. Other times, it could be installed by an application acting as another form of malware, such as a trojan or spyware.

While there are applications designed to detect and remove adware, since it is not always installed separately to an application these applications may not always be able to remove all adware.


What is a Rootkit?
A rootkit is an form of malware that installs itself at a very deep level of the operating system, and as such can prove itself very difficult to remove. They are often designed to take advantage of, or change the operation of fundamental functions the operating systems provides. Rootkits can be used to change the behaviour of an operating system, to allow other forms of malware or other attackers access to the system, or to perform the functions of other types of malware at a level that is very difficult to detect.

Rootkits are not always designed to do bad, however, and some security software can use rootkits or rootkit techniques to hide themselves from forms of malware designed to remove security tools.