I recently made a post about an audio steganography program and had another concern I thought I might ask. I understand that most music has DRM in them. If I hide secret files in audio files with DRM can an adversary see that I have hid files in it because of that? Also, wouldn't this be breaking the law as well because I'm technically modifying that file?
You probably mean watermark rather than DRM. DRM forces you somehow to use subject in accordance to the license.
Watermark (signal modified using the steganography) can be supporting technology for DRM (i.e. you can't hear audio when PlayStation detects that movie is not legal - based on audio steganography watermark it prevents you to watch the movie).
As far as I know, it is very hard to find steganography data in any kind of media, because you have to know the algorithm used to encode the data to the signal.
What you definitely can do is you can compare original signal with modified one and based on these data to try to analyse if there is some pattern in it.
Good math guy can maybe make it :)
Regarding the law (European one), when I buy a CD nobody can tell me anything when I make a backup copy in any form (i.e. MP3). Also, when I put some hidden data to it it is my problem.
For distribution it will depend on the license the owner of rights will provide. If they will say you can't modify, you can't do that ;)