There are thousands of common forms of spyware. Many of them primarily act as spyware, whereas other programs contain features of spyware. Below are the various instances of frequently observed spyware forms and their characteristics:
Browser session hijack: This spyware tries to modify the browser settings of the user. There are various ways to install them. However, the main intent is to modify the browser behavior in such a way that, the user directs to the sites of the spyware author's choice instead of the sites that the user normally wants to reach. Often, they redirect lead users to the advertisements. They earn commissions from the hijacker, the moment any unsuspecting surfer pays a visit to their sites.
Cookies: Cookies are small packets of information that are stored on the system of the user by the web server. Because of subsequent visits, most web servers can retrieve such cookies. Very often, they store user authentication, other types of user state information and preferences. This is because they are helpful to store user identification information. This differentiates one user from the other. In addition, they also track the user across more than one web site. With the help of correlations and other techniques such as web bugs, they build profiles of individual users that may or may not contain personal information.
Web Bugs: On the other hand, web bugs are HTML elements that take the form of image tags. They retrieve information from a particular website. When the image is invisible to the user, the request making act may provide vital information about that user.
Some Web bugs often embed themselves in HTML enabled email messages or in web pages. Even the links track the previously set cookies or unique strings embedded in the URL. The typical use of this is to log the successful delivery of the messages to the unique email address. Once the user accesses the image, the cookie is set and is associated with the other email address as the beginning of the profile. Then, the cookies track the portions of the browsing habits of the user.
Browser Helper Objects: They are common problems with the internet explorer (IE). They are inprocess4 COM objects specially designed to make IE extensible in nature. They also permit easy modification and/or addition of functionality. The moment the surfer starts the internet explorer, the installed BHOs get loaded into the process space of the browser. Although BHOs take the shape of the IE toolbar, there is no requirement to implement the visible interface.
Bots: They are a special class of malware. Also known as zombie, they are the largest malware problems observed currently on the internet. They are remote control agents installed on the multiple end user systems. Typically, these agents use some form of control channel and command.
Autonomous Spyware: It either operates as a simple process or injects itself into the other processes that run on the system. It often begins at system startup or user log on.
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