How To make files FUD???

Hex (Hexadecimal) is the way of representing data. In computer science, hexadecimal means base-16 numbers. These are numbers that use digits in the range: 0123456789ABCDEF.

Hexing is the the process of modifying application files using Hex editors (software's used to edit files in hex format).

How Antivirus works???

First of all, lets know how antivirus flag any file as virus.

Antivirus works in a pretty complex way. To summarize its working in short, antivirus has virus definitions (also called signatures) stored in its database. While scanning a file, Antivirus searches for these virus definitions or signatures in a file and if it finds these signatures in a file, it flags these files as virus.

Hexing to make Trojan virus undetectable:

Now, when you know all the basics, its time to know what you have to do to make virus                                                                                                     undetectable.

When you have created the virus file, simply open the virus Trojan file in Hex editor and search for signature which Antivirus has flagged as virus definition. We have to change this signature such that it will not affect the working of our Trojan virus.

There are many techniques used to search for virus signature in file and even change these signatures. You can do this manually or even by using software. Once you have successfully changed this signature, antivirus will not detect your Trojan virus, thus making this virus Trojan FUD.