Why Computer Antivirus Software Often Fails To Prevent A Trojan Horse Infection

One of the first things most people ask themselves when faced with an infected computer and a costly computer repair bill is why their antivirus program didn’t prevent it. While antivirus software is good at preventing the computer from becoming spontaneously infected with a traditional computer virus, it can do little to stop a trojan horse given the nature of what a trojan horse actually is. To understand how to keep a computer from becoming infected with a trojan it is first necessary to know the difference between a virus and a trojan horse.

Computer viruses have been around for a very long time and generally take advantage of security holes in the computers operating system or the software that runs on it. By taking advantage these security flaws commonly found in computer software, computer viruses are able to spread from computer to computer entirely on their own; much the same way that a human virus such as the flu spreads from person to person. Antivirus software is programmed to recognize what a virus infection looks like while it’s happening and takes steps to prevent it.

Trojan horses on the other hand are programs that the operator of the computer installed on the machine themselves. In most cases this happens after the owner of the computer has been tricked into installing something that appeared to be something else. Trojan horse programs got their name from the Trojan war and the large horse that was built to look like a gift and was brought into the city when it was actually filled with enemy soldiers. A trojan on a computer works much the same way. In most cases the trojan has been designed to look like an update for software that the computer owner recognizes and is already installed on the computer such as Java or Flash. While surfing the internet it is inevitable that at some point we will all visit a web page site that has been infected with a trojan horse. The infected web site may display a fictitious warning that the Java, Flash or other software on the computer is out of date and needs to be updated. The infected web page then displays a link for the unsuspecting person to click on where they will presumably be able to download and install the latest version. When the link is clicked on it will download the trojan onto the computer and give the unsuspecting user instructions to install it. It then appears that the latest version of whatever software program that the trojan claims to be is being installed when actually it is really installing something that will damage the computer– or worse yet lock the user out of their own computer and demand a ransom payment to unlock it. For this reason most operating systems such as Windows XP, Windows 7 or Windows 8 will display an added security warning telling the user of the computer that a program is trying to make changes to the computer and then ask the user if they want to allow it. In many cases the unsuspecting person doesn’t realize that they are installing malicious software on to their machine and gives the trojan horse permission to install. Since the computers owner is giving the trojan horse permission to install there is little that traditional antivirus programs can do to prevent it.

By understanding the difference between a trojan horse program and a virus it is becomes much easier to understand why computers become infected with trojan horses in spite of having up to date antivirus software. Keeping a computer clean and free from trojan horses has more to do with prevention than having the latest up to date technology. As a rule of thumb it helps to be mistrustful any time a web page asks you to install something; even if it’s something that you seem to recognize.

Jason Roskopf is a Waukesha computer repair and IT services expert and Owner of the “IT Connect” Milwaukee computer repair service centers.

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