Adware

Adware
Adware or advertising-supported software is any software package which automatically plays, displays, or downloads advertisements to a computer after the software is installed on it or while the application is being used. Some types of adware are also spyware and can be classified as privacy-invasive software.

Advertising functions are integrated into or bundled with the software, which is often designed to note what Internet sites the user visits and to present advertising pertinent to the types of goods or services featured there. Adware is usually seen by the developer as a way to recover development costs, and in some cases it may allow the software to be provided to the user free of charge or at a reduced price. The income derived from presenting advertisements to the user may allow or motivate the developer to continue to develop, maintain and upgrade the software product. Conversely, the advertisements may be seen by the user as interruptions or annoyances, or as distractions from the task at hand.

Some adware is also shareware, and so the word may be used as term of distinction to differentiate between types of shareware software. What differentiates adware from other shareware is that it is primarily advertising-supported. Users may also be given the option to pay for a "registered" or "licensed" copy to do away with the advertisements.

Adware can also download and install Spyware.

Well-known adware programs/programs distributed with adware
123 Messenger
180SearchAssistant
888bar
Adssite Toolbar
AOL Instant Messenger
Ask.com Toolbar (Toolbar is automatically installed with many different programs, even after you uncheck Ask.com during the installation process.)
Bearshare
Bonzi Buddy
BlockChecker
Burn4Free
ClipGenie
Comet Cursor
Crazy Girls
Cydoor
Daemon Tools - (Software comes bundled with the "Daemon Tools WhenUSave Toolbar" but can be unchecked during installation)
DivX
DollarRevenue
eBike Insurance
eCar Insurance
eVan Insurance
Ebates MoneyMaker
ErrorSafe
ErrorSweeper
Evernote
Ezula
FaceGame.exe
FormatFactory
Foxit PDF Reader
FlashGet
Gamevance
Gator
Gool.exe
IWNet
Kazaa
Kiwee Toolbar
Messenger Plus! Live - (Software comes bundled with adware, but can be unchecked during installation)
MessengerSkinner
Mirar Toolbar
Oemji Toolbar
PornDigger!
Smiley Central
Spotify - (A subscription can be paid to remove ads.)
TagASaurus
TopMoxie
Tribal Fusion
Videothang
Viewpoint Media Player
VirusProtectPro
Vuze
WeatherBug
WhenU
WinAce (now with MeMedia AdVantage)
Windows Live Messenger
Winzix
XXX Shop online
XXX Toy
Yahoo! Messenger
Zango
Zango Toolbar
Zwinky
The Eudora e-mail client is a popular example of an adware "mode" in a program. After a trial period during which all program features are available, the user is offered a choice: a free (but feature-limited), an ad-supported mode with all the features enabled, or a paid mode that enables all features and turns off the ads.
Refer to http://en.wikipedia.org/wiki/Adware