I forked a repo on GitHub. A few weeks later a DMCA take-down notice was issued against the repo (and all forks). Someone claimed the repo had stolen their copyrighted stuff.
Unfortunately, I couldn't verify whether the claim was correct because I wasn't provided with a copy of the original copyrighted material. So it wasn't possible for me to tell if the DMCA was genuine or not. I suspect the DMCA claim was valid but it was impossible for me to tell.
GitHubs process around the DMCA did not fill me with joy.
It does publish the DMCA notices at https://github.com/github/dmca, which is a lot more transparent than most companies.
At the end of the day GitHub has to comply with the law, whether they like it or not. And looking through that list of DMCA notices many of them seem fairly valid on the face of it.