The main target of spyware is undoubtedly Microsoft’s Internet Explorer. It is the most widely used web browser and has a long history of weak security. It is deeply integrated into the Windows operating system and its scriptability makes it highly susceptible to malicious software intrusion. Browser helper objects can be easily attached to Internet Explorer. These helper objects redirect traffic and add toolbars.

The most common reason that users of the Microsoft Windows operating system seek technical support from Internet service providers or computer manufacturers is a spyware infestation. In most cases, the user does not understand spyware and believes that system stability, performance, and/or connectivity issues are related to Microsoft Windows, hardware, or a virus. Sometimes, owners of severely infected systems end up buying a completely new computer system because their existing system “has become too unreliable or slow.” Heavily infected systems sometimes require a clean reinstall of all your software to allow the system to function properly. This is a time-consuming task, even for experienced users.

Normally, a single piece of spyware will not disable a computer. However, an infected computer almost always has more than one piece of spyware installed. AOL conducted a study in 2004 and concluded that if a computer has any type of spyware on it, it will be infected by dozens of different pieces. It is the cumulative effect of the different spyware components that causes the problems reported by users. The computer slows to a crawl, dominated by the many power-hungry processes running on it. Similar to an immunodeficiency disease, some types of spyware disable antivirus software and firewalls and/or lower browser security settings, subjecting the system to additional infections. In addition, there have been cases where a spyware program has disabled a competitor’s spyware program that was already installed on the computer.

There are some forms of spyware that modify system files so that they are very difficult to remove. For example, Targetsoft changes the Windows Sockets “Winsock” files. Removing the spyware-infected file “inetadpt.dll” will interfere with your network usage. For convenience, a Windows user generally has administrative level system privileges. Because of this, any program the user runs, intentionally or not, will have full access to the entire system. Spyware, along with various other dangers, has caused some Windows users to switch to other platforms, such as Apple Macintosh or Linux, which are less frequently targeted by spyware authors.

The most common complaints about spyware are pop-up ads. Displaying and/or downloading advertisements can overload a system. It is very rare for an infected system to have only one spyware program running. More typically, the system will be infected by dozens of applications. So while one of the programs may infrequently display ads, the cumulative effect on the system can become overwhelming.

Most web users do not like offensive or irritating advertisements. Like banner ads, some SpyWare ads use flashing banners or animations designed to attract the user’s attention, making them very distracting. Pornography pop-up ads are often displayed indiscriminately, even when children may be using the computer, which violates many anti-pornography laws.