Adware is software that displays advertisements on your computer.

Adware, or advertising-supported software, displays advertising banners or pop-ups on your computer when you use the application. This is not necessarily a bad thing. Such advertising can fund the development of useful software, which is then distributed free (for example, the Opera web browser).

However, adware becomes a problem if it:

• installs itself on your computer without your consent
• installs itself in applications other than the one it came with and displays advertising when you use those applications 
• hijacks your web browser in order to display more ads
• gathers data on your web browsing without your consent and sends it to others via the internet
• is designed to be difficult to uninstall.

Adware can slow down your PC. It can also slow down your internet connection by downloading advertisements. Sometimes programming flaws in the adware can make your computer unstable.

Advertising pop-ups can also distract you and waste your time if they have to be closed before you can continue using your PC.

Some anti-virus programs detect adware and report it as “potentially unwanted applications”. You can then either authorize the adware program or remove it from the computer. There are also dedicated programs for detecting adware.