Spyware is unauthorized software that is installed on your system when you click on an unknown or unsafe link. Once you click, a software application is installed on your computer system without your knowledge, and it can be used to invade your privacy.

Spyware is typically distributed by hackers who are paid for every user's system they contaminate. Lurking mostly on open forums and unregulated sites, hackers will usually entice a user with a message like "come and see my picture". When the user clicks on the link, they normally get a message like "come back later to see my picture". The message is fake, but once the link has been clicked, the system contamination is all too real.

A software program that collects information about your web browsing habits in order to display strategic ads on your web browser, or imbeds ads directly into your existing software without your permission.

Scumware often alters the content of websites you are accessing, changing the normal links to re-route you to other websites. They can also broadcast information that you submit in forms, it can create more pop-up windows in your browser, it can track each and every single website that you visit, how long you stay, and which links you clicked on. Most of the time scumware hides itself on your computer in multiple locations to hinder the removal process.

Phishing is a criminal activity using social engineering techniques. Phishers attempt to fraudulently acquire sensitive information, such as passwords and credit card details, by masquerading as a trustworthy person or business in an electronic communication. Phishing is typically carried out using email or an instant message, although phone contact has been used as well.

Dialers are a type of software typically used by vendors serving pornography via the Internet. Once dialer software is downloaded, the user is disconnected from their modem's usual Internet service provider, re-connected to another Internet service provider (new dial-up telephone number), and the user is billed at exorbitant rates. Dialers do not "spy" on their intended victims, but these malevolent programs can rack up significant long distance phone charges, costing victims time and money.

Malware is short for malicious software. Malware is software designed specifically to disrupt a computer system. For example, a trojan horse or a virus is considered malware. Some advertising software can be malicious in that it can try to re-install itself after you remove it. Basically, it is virus ware.

Toolbars can be downloaded to your web browser to make browsing easier. Examples are Google, Alexa, and Yahoo toolbars. Even though these toolbars are very handy to use, these toolbars have the ability to track everything you do on the Internet and to pass that information back to the owners of the toolbars. Be cautious to read the terms and conditions page before you download any toolbar.

A drive-by download is a program that is automatically downloaded to your computer, often without your consent or even your knowledge. Unlike a pop-up download, which asks for consent (albeit in a deceitful manner likely to lead to a "yes"), a drive-by download is carried out invisibly to the user. They can be initiated by simply visiting a Web site or viewing an HTML email message. Frequently, a drive-by download is installed along with another application.

Cookies are small pieces of information that are generated by a web server and stored on your computer for future access. Cookies were originally implemented to allow you to customize your web experience, and still continue to serve useful purposes in enabling a personalized web experience. However, some web sites now issue adware cookies, which allow multiple web sites to store and access cookies that may contain personal information (including surfing habits, user names and passwords, areas of interest, etc.), and then simultaneously share the information it contains with other web sites. This sharing of information allows marketing firms to create a user profile based on your personal information and sells it to other firms. Adware cookies are almost always installed and accessed without your knowledge or consent.

Browser hijackers are programs that run automatically every time you start your Internet browser. These hijackers can sometimes control your browser, like Internet Explorer. Some Browser Helper Objects are really good for expanding your browser capabilities, but there are others that may not need your permission to install and which can be used for malicious purposes like gathering info on your surfing habits. This can cause anything from incompatibility issues to corrupting important system functions making them not only a threat to your security, but also to your systems stability.

A software program that traps every keystroke you make to capture information such as user names, passwords, and critical financial information like credit-card numbers.

A destructive program that masquerades as a helpful one on your computer. Once a Trojan horse is allowed into your system, it pops up countless ads that claim to rid your computer of viruses but instead introduce viruses onto your hard drive.