[pbhjpbhj]

It's a pretty big search space but one presumably could brute force it and create a site having links to all/lots of unlisted content.

[duskwuff]

As mentioned in another comment on this post, the search space is 2^64 IDs large. It's not practical to find unlisted videos via "brute force".

[ItsMe000001]

Yes... and your point is? :-) Especially, what's the relation to my comment? As I said, it is not supposed to be "secret" pr "secure" at all.

[pbhjpbhj]

That was the entire point, it wasn't a contradiction, merely a reflection. I've read the OP now, seems that one of the sites mentioned has done just that.