What is The Difference Between Adware and Spyware?

When people speak about the different forms of malicious computer software, they often group adware and spyware together. However, these two forms of malware -- though equally damaging -- have different effects on a computer. Has your computer behaved strangely recently? Has its performance suddenly decreased? Are you seeing unusual pages in your browser? Your computer may have an infection. Understanding the effects of these two common forms of malware can help you diagnose an infection and get your computer cleaned up before the infection causes further damage.

What Is Adware?

Some people -- students and supporters of open-source software, to name two examples -- create free software without any hope of immediate financial gain. Some people hope to obtain jobs in the software industry after gaining experience, and others simply want to create useful tools that improve people's lives. Most of the time, though, software developers release free tools because they want to monetize those tools in ways other than direct sales.

Advertising -- when implemented with full user disclosure -- is a completely legal way to support free software. Free software can support itself by displaying advertisements during installation, during usage or both.

Ad-supported software becomes adware when its only purpose is to display advertisements without serving a useful function or giving the user a good experience. Ad-supported software is malicious if it displays an error message when you attempt to uninstall it. If your browser constantly displays pop-up advertisements when you attempt to surf the web, your computer probably has an infection. Particularly malicious forms of ad-supported software may even plant affiliate cookies for popular merchants such as Amazon.com and eBay.com in your browser. Every time you purchase a product online, the creator of the malicious software receives a commission that he or she didn't earn.

What Is Spyware?

On the Internet, information is perhaps the most valuable of all currencies. A company that knows your browsing and buying habits knows exactly how to advertise to you. Major corporations often provide free tools in exchange for the ability to gather information from users. Google's popular Gmail service is one example; Google scans your messages for keywords to enhance the effectiveness of its advertisements.

If a computer program scans and reports on your activities without your permission, it is spyware. This form of malware can hide within software that appears legitimate and safe. Your browser can also download it without your knowledge if you visit a hacked or malicious website.

Software designed to spy on you can have a variety of negative effects. Sometimes, this type of malware simply tracks the websites that you visit. In extreme cases, though, it may record your keystrokes to harvest your banking, email and social media passwords. If you have ever seen strange activity on any of your online accounts, malware could be the cause.

Malware has to use system resources to collect and transmit information about your activities. It also often needs to exploit a vulnerability to infect your system. If your computer suddenly seems slow or displays unusual error messages, a malware infection could be the cause.