No. You can basically always decompile proprietary software and work out how it works. And even publish most of your findings. In some places like the US, if that code is DRM its now illegal to study (Under the DMCA specifically I think).
Is there a specific definition that makes something DRM?
Sounds like all software companies should add some trivial DRM only for the specific purpose of exposing people to legal risk if they attempt to reverse engineer their code.
