It doesn't seem to contain much info about the infection technique/ deployment. Everyone can write a backdoor but getting the backdoor in is the real challenge and the interesting part.
Not a native english speaker, but "never-before-seen" doesn't sound right, shouldn't it be "never-seen-before"?
It is legit, but it's rare and old-fashioned.
Yup, it is legit but old
But more common than never seen before in this context.