The Difference Between Spyware & Adware

Spyware and adware are often both classified as malware. They're two different things, and adware may or may not technically be malware. It's not uncommon for a malicious program to be both spyware and adware. Both spyware and adware can have unexpected and undesired effects on the operation of your computer.

The Facts

Spyware is installed on a computer without your informed consent. Its purpose is to collect information about you. This information may relate to your web browsing and computer-use habits, or to you personally. A legitimate-looking program you intentionally install may contain spyware you didn't know about.
Adware is simply any software containing advertisements. These ads may appear in the program itself, in pop-up windows or as other downloads. The advertising may simply be the price you pay for use of the software, or it may be installed along with a legitimate-looking program without your realizing it. Some adware is also spyware.

Identification

Whether a program is specifically spyware or adware is often a moot point. Spyware and adware may both adversely affect your computer's performance. They may cause pop-up windows, redirect your web browser to pages you did not intend to visit, cause your web browser to operate incorrectly, download additional software onto your computer, and slow your computer's overall performance. If you plan to download and install an application on your computer, it's important to do enough research that you're reasonably sure the program will not have these effects. To do this type of research, search the Internet using the name of the software you intend to install (enclosing the name in quotation marks will make your search easier) and the words "spyware" or "adware." The search results should tell you not only how the software provider feels the program is classified, but also how other people (end users and computer experts) feel about it.

Features

Adware is designed to cause you to visit websites or obtain software or products based on advertising. There are some reputable programs (e.g., Eudora) that offer an advertising-supported version as an alternative to a version you pay for. Adware can also direct you to products and web pages that match your interests, based on web browsing you've done.
Spyware is, by definition, installed without your informed consent. As such, its features may mimic those offered by adware, but without your having any choice in the matter. On the other hand, its primary feature may be to funnel information straight back to some third-party source. This information can then be used for attacks upon your privacy or for more targeted advertising or unwanted programs on your computer.

Considerations

Always determine whether a program is considered adware or spyware before you chose to install it. If you find it identified as such and want it anyway, do a web search to determine if other users have experienced problematic side effects and consider whether it's worth the risk before you install it. Once installed, both spyware and adware can be difficult to remove. Some programs will offer an automated removal process. Others will offer such a process, but the process itself may be poorly written and not work correctly. Still others offer no removal process and may make changes to your computer specifically designed to prevent you from removing them or undoing any changes they make to the settings on your computer.

Prevention/Solution

If your computer exhibits symptoms of being affected with malware of any kind, including spyware or adware, you'll want to try a two-part removal process. First, go to "Add or Remove Programs" and try to uninstall the problem program. Depending on the program, this may or may not be possible. Some malware will prevent you from even opening "Add or Remove Programs."
Now download a reputable malware remover, install it, update it and run it. Even if you were able to uninstall the malware with the first part of this process, you should run a malware remover---it may remove additional malware you weren't aware of. Reputable malware removers include Spybot Search & Destroy, Ad-Aware, and Malwarebytes Anti-Malware.

References

• Spybot Search & Destroy
• Ad-Aware
• Malwarebytes Anti-Malware