There of course exist many different types of computer viruses and other malicious software. One of the oldest of most prevalent type of virus is known as the Trojan Horse - it's namesake, of course, coming from the legendary Greek myth in which a gift turns out to be an attack from the inside. There are different types of dialer viruses, but the Trojan horse dialer is the most common. The principle on which a Trojan horse dialer works is to infect your system in a tricky and innocent way: by posing as a legitimate piece of software.
The Trojan dialer will infect your system with a dialer virus by posing as a normal and helpful program and asking you to install it. Once installed, the Trojan dialer will begin to use your modems to make calls without your permission, and often to numbers that create a high charge on your phone bill.
The started way a Trojan dialer will infect the typical users system in when they find themselves on a website that presents them with a pop-up window, this window will generally be posing as something else. The most common Trojan dialers will be disguised as some kind of small utility. Often the user will be presented with a pop-up window that tells them their PC is running slow, and they should click YES to fix it, or that their system is insecure and they should click YES in the windows to fix it.
The Trojan dialer window can be a little tricky for the novice user because the application is not installed in an obvious way. The YES button that the user clicks often installs the software, although it is disguised to look as if it is a normal prompt button which the user encounters everywhere while surfing the net.
Once the Trojan dialer has snuck its way into he user's system, either by posing as a legitimate piece of software is coming "bundled" with another applications, it will begin to make calls in the background, unbeknownst to the user. Often the user will not realize they have a Trojan virus until they see the high charges on their phone bill. It is not always clear what the motivations are of creators of a Trojan dialer, in same cases, the dialer will simply call expensive numbers like sex lines for the purely malicious intent of costing the user money.
Although Trojan dialers are prevalent throughout the internet, the average user should have no reason to give them much thought: antivirus software properly installed is able to seamlessly eliminate the risk of a Trojan dialer infecting the system of an average PC user. If you take the proper precautions by making sure your virus software is up to date and running properly, you should find that Trojan dialers pose little threat to the integrity of your machine. The most common antivirus solutions which should simply eliminate Trojan dialer threats are Symantec antivirus (commercial) and AVG antivirus (Free) - using either of these systems Trojan dialers can be eliminated easily.
The problem occurs when a user fails to install or properly update antivirus software, and this is the type of user that the Trojan dialer virus will most likely prey on.