On TV there are commercials. On a computer, there is adware, programs that advertise for things unrelated to the featured site.

Given this definition, it's not hard to realize there is benign or even (arguably) good adware. These programs manifest as advertising blocks on certain websites that allow that domain to be free for the host and/or the service to be free for the user.

Some adware is just as benign, but its instillation skirts an ethical borderline. These adware programs will come bundled with other software but won't state their presence upfront. Sometimes the agreement to post ads will not appear in the download wizard, and sometimes it will only appear buried in the End User License Agreement (the long I Accept contract that few read in full or not at all.)

Finally, there is adware that is undoubtedly malware. This variety is installed unwittingly by a user or comes secretly bundled to another program. The secretive nature of this adware thus gets it categorized as a type of Trojan. These are the most notorious. They do things as invasive as hijacking browser windows to steering you to websites or unspecified homepages. The most well known of this type is the classic popup, an unrequested ad that flashes over other windows. Not only are these types of adware frustrating, due to the unscrupulousness of their installation, these programs often don't come alone and are accompanied by other forms of spyware that monitor your web use.

Backdoors are a particularly dangerous form of Trojan. Once a backdoor is installed on a computer, it allows another user (called a master) to monitor the actions of a computer as well as install a remote access utility. This is a utility that allows access to the computer, its files and commands, and thus the ability to control these things. Remote access is something that system administrators and tech supporters use legally to help set up and repair systems on your computer. Like people using a remote control, these people can access your computer via LAN or the Internet from across town or across the country. A backdoor allows a master to illegally monitor and even control your computer the same way without asking your permission. Consequently a master can

• view confidential information
• execute malicious codes
• launch programs
• send / receive date via the Internet
• delete files and other data
• display notifications
• reboot the system

This means that a single backdoor can facilitate tasks which are usually accomplished by several smaller Trojans. And since masters do not want you to know they are there, they will often be discreet, stealing information without your knowledge. Since many backdoors are not visible in the log of active programs, they are hard to detect.

As their name implies Browser Helper Objects (BHOs) assist a web browser (usually Windows Internet Explorer) in doing some specialized tasks. For example, the plug-in that allows IE to open an Adobe PDF is a BHO, as is the Google Toolbar for IE. But just as with most legitimate programs, illegitimate versions exist as well.

Since BHOs have an unlimited access to the Internet Explorer event model, some malicious programmers have made malware that uses this feature to their advantage. Some BHOs, such as the MyWay Search Bar, would track user activities and then sell that information to 3rd parties. More insidious BHOs are capable of installing Trojans that work in tandem. Download.ject was a famous attack that downloaded a keylogger into the user's computer and then used a BHO to detect whenever a user accessed a secure site. With the keylogger they could track keystrokes to determine what passwords were being entered.

Commercial RAT (or Remote Administration Tool) is not always a bad thing, but when a commercial RAT product is used to remotely administer a user's computer without that user's consent or knowledge, it can turn into an ugly situation. If a commercial RAT program is installed on your system and controlled by an unscrupulous hacker, he or she can shut down programs, delete files and steal all of the information on your hard drive. Commercial RAT attacks may very well be one of the most dangerous spyware risks lurking on the Web.

Data miners are programs that collect data from your computer (such as email addresses, web searches, etc.) and then transmits the data to a third party. Some cookies are data miners, but many cookies are harmless. The cookies that act as data miners can be considered Spyware applications.

Initially the word dialer referred to any programs in a computer that allowed an analog dial-up modem to connect to a phone line. Such programs are necessary for all non-broadband Internet use. However, the word today usually refers to a specific type of fraud that uses a dialer to connect a user to a premium number (equivalent to a 1-900 number) at outrageous cost.

Sometimes the dialer will advertise access to a multitude of special contents. These could include illegal MP3 downloads, pornography, or illegal hacking materials. The most insidious dialer programs though, look for security holes in the settings of a user's OS and change the dial-up numbers to premium numbers without telling the user. These unscrupulous dialer dealers will often have agreements with these premium sites to take a percentage of the profit.

A downloader does exactly what its name implies. This program is a the part of the Trojan that actually downloads the malicious software onto a user's computer. From there, the downloader either launches the malware or registers it in the local operating system requirements so that it will automatically run at a specified time or after a specified action. Sometimes the locations and names of the malware being downloaded are sent from an unseen website, but sometimes they are actually encoded into the downloader itself.