Roughly 3-4 years ago, we hired a PHP developer and tasked them with building small "satellite" websites. They didn't stay long, and we had largely forgotten about them.
Fast-forward to today, one of the sites became big - we've since rewritten the whole thing in another language and open-sourced it on GitHub.
However, now we've found the entire PHP source code of the old site on GitHub, uploaded to the ex-employee's personal account at a time when they were still working with us.
Nobody at the company knew about this or authorized it, not even my boss. It's likely that the ex-employee uploaded it as a "test" without fully realizing what GitHub was. There is no LICENSE or README in the repository.
It would be very difficult to contact the ex-employee, and they might not remove it anyway - so how do we get GitHub to take it down quickly?