As we hear words spyware, malware, adware or something like that we start thinking about harmful and illegal programs. But that's not true. Yes, malware can damage your computer system and spyware can steal your identity and it's not legal. But adware has totally different functions. This program is for advertising purposes. When you get annoying pop-ups this is the moment when adware works.
And if malware and spyware are often illegal, adware sometimes is legal. Legal adware programs are useful for users, when they help to fill in online data forms, remember some user names and passwords. Although it brings advertisements it's legal because adware like that is often governed by a licensed agreement. This agreement acknowledges user about programs installation.
Legal adwares do not violate a Web site publisher's trademark or copyright if their pop-ups and advertisements appear on separate window and are labelled. And it's legal until the adware clearly states to users that they are getting free or reduced-price software in exchange for receiving marketing messages. Companies like Claria and WhenU are legal adware provider.
But the opinion about legality of adware is very ambivalent, because even legal adware tracks user behaviour and buying habits for the company's customers. Some of programs are bundled with other software that affiliates user's computer without hi's permission. And removing them might cause many damages to other important programs.
So there are many questions if adware is legal or not.