Significance

Most adware gets bundled with many popular, free programs. The advertising revenue from adware allows the makers of freeware software to give programs away while still making a profit.

Effects

Most adware programs clog computer resources in order to run themselves and hog Internet connection bandwidth querying their server for new ads. In addition, some adware causes problems with the operating system because the programmer does not need to take quality into consideration since much adware goes unnoticed.

Typical Programs That Include Adware

Adware often resides in programs that add themes to the desktop or mouse pointer, free computer games, file sharing utilities and weather and news tool bars.

Misconceptions

Not all adware programs are considered malicious. Those that are upfront with their presence and ask permission to install themselves, along with an option to uninstall the adware, are viewed as good--they are necessary to fund some programs and cause few problems. Bad adware programs hijack a computer and try to prevent the user from uninstalling it.

Prevention/Solution

In the case of malicious adware, sometimes only special software can remove ad programs. Some anti-adware programs, such as Lavasoft's Ad-Aware, are free and highly effective at removing adware.

Source:

TopBits.com: Adware

SpamLaws.com: What is Adware (Other Than Annoying)?

More Information:

Lavasoft Ad-Aware