I have already given enough information about trojans in my last article. So I won't go in the intricacies here. I suggest you refer to that article. Before doing things of any sorts, a small warning. Handling trojans is a dangerous thing, so I don't suggest you to download them without having complete understanding of their utility and power. So read on.
Here I will try to inform you on the ways you may be infected by a trojan horse. Pay attention since if you take these precautions, it will be virtually impossible for the hacker to infect you with one.
The most simple method is to send a trojan via email. So you receive a message saying that a wonderful file is attached and it will coerce you to click on it. This one is for dumb heads. I assume you are not one of those who click every attachment without scanning it with an up-to-date AV.
Secondly, you may receive a file from someone you know and the file looks harmless enough. On clicking you find a small application running, so you rest assured that the file was not a trojan. Here is where the ingenuity of the hacker comes into play. What he does is that he joins the trojan horse with an harmless application. . Such joiners are widely available on the Net. (If you want one, try Joiner). He designs a new icon for it using Micro Angelo. If he uses sub 7, the best and the most dangerous trojan according to me, then the latest version comes with an inbuilt icon changer. So one can easily assign a mp3 icon to a sub 7 server. (More on sub seven later)
If you are an experienced net user (I assume male, though I am not gender biased), you can easily restrict yourself from falling prey to above methods. But can you resist the feminine charm? This is one of the most widely used and successful means to catch a prey who is not a fool. For this, you need ICQ (I don't need to tell you about this, right?). So you may meet someone on random chat claiming to be a sultry babe from Amsterdam. She arouses your erotic senses and then says that she wishes to send you an erotic photo of herself. Naturally, no male (Here I am talking about normal males, not those rare ones who can resist such a temptation) would like to miss such an opportunity. So you get an incoming file request, say pic.jpg. Now you know that trojan has to be an .EXE file, so this cannot be one. So you receive it and click it.
The file is indeed a Jpg file joined with a trojan. But it is a fact that though you can bind an exe file to a Jpg one, the final file has to be an exe. What the hacker does is that he renames the file as pic.jpg.exe. ICQ shows this as pic.jpg. So you end up making a fool of yourself.
These are not the only ways. New ingenious ways are being designed by thinking minds to get better of you. So keep your senses wide awake when dealing with someone unknown on the Net.
Next time, we will have a look into the working of a trojan horse, it's general features and it's capabilities. So till then bye and safe surfing.