To make a trojan undetectable to the antivirus, you need to know assembly code. The way you would make it undetectable would be:1. Somehow find the strings of code, or "signatures" included in all antivirus programs to detect viruses and trojans.
2. Find the signature of the trojan you wish to make undetectable,
3. Try to find this string of code inside your trojan by splitting it.
4. Then disassemble it and insert a few extra bits of code that would not affect the program, but would change the detectable part of code enough to make it unrecognisable to the AV.
Now, the trojan would be undetectable, because you have modified it enough for it not to be recognised by the antivirus. Of course, this is an extremely complex thing to attempt, and I don't even know any assembly or machine code, so there are definitely more things you would have to do than I have described, I am just not experienced enough to know about this. So I doubt you would be able to make a trojan undetectable, to do that you have to know machine code and assembly, which is much harder than normal programming languages like c++ because machine code is directly interpreted by the processor, you have to know about how antivirus programs work, and you have to have the right tools to use, like disassemblers etc. So basically, it's not as simple as "here, download this program and it will make all your trojans undetectable", you have to have a lot of knowledge and experience to be able to modify binary programs. If you really wanted to know, you could probably ask some of the admins and moderators of this forum, they might know, although they wouldnt help you if you said you were doing this to a trojan.
