Adware is software which is designed to serve advertising to the computer user. Some adware may also be spyware if it contains the ability to gather information about the user. If adware only serves ads, it is not technically spyware. Adware is legal so long as it is installed without hacking. The act of unauthorized hacking is illegal in most places.

Adware Justification: Adware vendors try to justify the use of adware as a means to recover programming costs for the creation of free or low cost utility programs. This is practiced as part of a claimed effort to hold pricing down.

Adware Installation Methods:
The adware may have came with another program installed by a user. When the program is installed the computer user may have been informed. If the computer user was not informed that the adware program was installed the action may not have been illegal, but companies that install programs without user knowledge are considered to be untrustworthy.

The adware may have been installed through a hacker tool or by using a computer hack. This method may use a vulnerability or unsecure configuration setting on the users web browser to install the program when the computer user visits a web page.

How adware ads are displayed:
Adware ads are usually displayed using pop up windows. Sometimes the advertising pop up windows will appear when the user is not actively surfing the internet. Advertisements may also appear in a bar at the bottom of the screen such as a search bar.

Damaging Characteristics of Adware:
Removal Prevention - Some adware programs are written to prevent their removal. The program may change system settings or system file associations to require the adware program to be able to operate the computer system or even run any executable program. Some adware can damage the user's computer software and hinder or disable the computer operation in this manner.

System Resources - Adware programs require processing power to run the program and will slow the computer and consuming additional internet bandwidth. Adware programs will request advertising pages from the internet and serve them to the user.

When adware is Legitimate:
Adware is only legitimate when the user is informed up front that they will be served ads. If the adware also gathers information about the user (spyware) it must inform the user of this to be legitimate. If the adware is designed to prevent its removal or was installed using a computer hack, it is not legitimate.