Нечто is like "a certain (something)". It exists only in nominative and accusative cases, "нечего" is not its genitive, as one may think, but means "nothing" as in нечего делать. That again is not the same word as ничего. (Bold letters = stress)

And the example sentence "пройтись по чьему-либо адресу" contains yet another word, "чей-либо", which I'd tentatively translate as "someone's, no matter whose".