I remember The Internet Archive celebrating the fact that the "do not tamper" clause was no longer legal for abandonware (as they host tons of abandonware that has been cracked, e.g. Win 95).
That's not how the DMCA works. Circumventing these measure is completely illegal. It's just that doing it on your own software is very unlikely to have anyone find out.
But it's a problem for researchers, who generally want to publish their findings (or at least was the last time I was really paying attention to the law in the early to mid 00s).
But I could be wrong.