Spyware

Overview
Spyware is software that gathers information (sometimes important information such as passwords) about a person or organization without their knowledge and has the ability to send that information to another person without consent or that asserts control over a computer without the consumer's knowledge.

How it Happens?
About.com elaborates on how Spyware is downloaded and what to do when it happens to you.

Bundled applications: Some types of spyware software are contained inside the install packages of other Internet software downloads. The most common form of bundling occurs with P2P software applications. P2P download files for installing Kazaa, for example, contain additional software packages like Cydoor inside the same file.

Spyware software can also be installed on a computer through download of: Each of these types of Internet download can result in anywhere from one to more than 10 different types of spyware software also being downloaded. Installing the primary application automatically installs the spyware applications, usually without the users knowledge. Conversely, uninstalling an application will often *not* uninstall the spyware software.
 * some less-reputable Internet Explorer browser toolbars
 * some so-called "agent" or "personal assistant" software like Gator, BonziBuddy and Comet Cursor
 * some packages promoted be "anti spyware" systems that in fact contain spyware software

What to do: To avoid receiving this type of spyware, carefully research online the functionality of a new software application before installing it.

Triggered download: Other forms of spyware software downloads occur simply by visiting certain Web pages in Internet Explorer. These pages contain script code that automatically triggers a spyware download as soon as the page is opened. Depending on the browser's version, security settings, and security patches applied, the user may or may not be prompted to accept/reject the spyware download.

What to do: To avoid receiving this type of spyware, either:
 * use the most up-to-date versions of both Microsoft Windows and Internet Explorer
 * use a Web browser other than Internet Explorer

What does it do?
Spyware can be a brutal virus that can take very valuable information from the user without a trace. These programs can ruin your system permanently. Microsoft.com elaborates on the consequences of spyware:

Knowing what spyware does can be a very difficult process because most spyware is designed to be difficult to remove. Other kinds of spyware make changes to your computer that can be annoying and can cause your computer slow down or crash.

These programs can change your web browser's home page or search page, or add additional components to your browser you don't need or want. They also make it very difficult for you to change your settings back to the way you had them.

How to Protect Your Computer Against Spyware
Nowadays, you can get relatively effective antivirus software free of charge. This programs will detect and warn the user when spyware or other viruses are about to be downloaded. Even if the virus sneaks through, most programs will assist you in removing it from your system. outlines a few below:

Panda Free Antivirus 2015 Panda Free Antivirus 2015 scores on par with the best commercial antivirus tools, both in our hands-on tests and independent labs tests. It's a new Editors' Choice for free antivirus.

Bitdefender Antivirus Free Edition (2014) You'll hardly know Bitdefender Antivirus Free Edition (2014) is present on your system, unless it quashes a problem. Its tiny main window and unobtrusive style are great if you want a strong, silent, and free antivirus solution.

Malwarebytes Anti-Exploit Free Malwarebytes Anti-Exploit Free shields your browsers against exploit attacks, even never-before-seen zero-day attacks. Give this unusual, free security tool a try.

360 Internet Security 2013 With an uncluttered user interface decorated in cheery pastels, 360 Internet Security 2013 is one of the better-looking free antivirus products. It performs its essential antivirus functions well, but an over-enthusiastic behavior-based detection system flags good and bad programs alike.

Ad-Aware Free Antivirus+ 11 The folks at Lavasoft gave Ad-Aware Free Antivirus+ 11 a total user-interface makeover and a new antivirus engine partner. The user interface is truly pleasing, a nice change. However, the product lost a little ground in malware blocking.