Adware is an application that looks quite harmful at the first sight or even does something useful but can contain mailcious code that will gather information and relay it to a third party over the Internet.

Adware are normally downloaded from download services in form of freeware or shareware programmes or may be smuggled onto one's PC via email messages, instant messages or the like. However, adware mostly requires human interaction to complete installation onto the victim's computer.

This happens often when one accepts the End User License Agreement during the application installation process.