I am incredibly amused by the person who refers to himself as a customer of this. If you want to be treated like a customer, find someone who will charge you money in exchange for the service provided.
The last post on another Yahoo! forum[1] is from an admin that says:
The new download issue which began 11/01/17 and returning an error 999 for most users is currently being investigated and we hope to have it resolved soon
This was before the TOS violation response was being returned so I'm assuming not everyone in Yahoo! was prepared to deal with this.
https://forums.yahoo.net/t5/Yahoo-Finance-help/http-download...
I am incredibly amused by the person who refers to himself as a customer of this. If you want to be treated like a customer, find someone who will charge you money in exchange for the service provided.