Money is the very crux of adware and spyware. These pose several problems and are a security risk.

Adware is a program that displays advertisements on the computer whether you want them or not. They are not just connected to particular websites or free software but are programmed to start up whenever your computer is switched on.

Programs like Eudora mail client display advertisements in lieu of charging registration fees for use of software. It helps developers recover program development costs. Kazaa the file sharing application comes bundled with at least three ad-ware programs. Two of them serve ads to the desktop while another redirects the user's browser to a search engine with advertiser sponsored web results. Well known ones are: BroadcastPC; Comet Cursor; GeoWhere; Network Essentials, 123 Messenger, Direct Revenue, and so on.

Unfortunately, other guises of adware are spyware and malware.

Spyware is a program code that relays information about you and your work without your permission or knowledge. Some just "spy" on you conveying your Internet habits to marketing companies, while others are "thieves" they access credit card information as well as other sensitive files. In plain terms, it is malicious software that can intercept or take control of a computer's operation without user knowledge or consent. Termed as "malware" the redefinition of spyware, the programs can:

Steal personal information and the address book.
Flood the browser with pop-ups.
Spam the system.
Slow down programs and connection.
Hijack the browser and redirect the user to a "con" page.
Uses the computer as a server to broadcast porn.
Can cause a crash.

Spyware reaches a computer through innocent web pages, game demos, MP3 players, search tool bars, and other downloads like free software. It installs itself and leaves a mark on the windows registry. It can hog the computer resources such as memory and hard drive and cause a crash or lock up. Keystroke-logging spyware can steal passwords and credit card information for thieves.

To protect the files one has to:
Use anti adware and spyware programs. Examples: Spybot, Search