Basically bypassing AV programs is like a game of cat and mouse, so backdoors might start getting detected at some stage, then the developers release an update, this will allow you to generate undetectable backdoors, then AV programs release an update which will make backdoors detectable ……..
So the main thing is to make sure that Veil or any other tool you’re using to generate the backdoor is up to date.
Here’s a few solutions to try if your backdoor is getting detected:
1. Make sure that you have the latest version of Veil, so do updated before doing use 1.
2. Experiment with different payloads, and experiment with different payload options and you should be able to bypass it.
3. Try generating a backdoor using the fat rat, empire.
4. Modify backdoor code if its in bat as shown in lecture 33.
5. Modify backdoor using a hex editor as shown in lecture 40.
6. Create your own backdoor (covered in python course).
The best thing to do is look at the last lecture of the course (bonus lecture) it contains all the courses that you can take with this course and a comparison between them.
Hope it helps!