The Pastebin poster claimed that the list he revealed was a partial list of Coinbase user emails and full names, and that the full list is much bigger. His next sentence perhaps gives a reason for the data leak: "Coinbase provides your full transaction history to the FBI, FinCEN and IRS every day. They are under a gag order."
"This list (the size of which is less than one half of one percent of Coinbase users) was not the result of a data breach at Coinbase," the San Francisco-based company stated in a blog post. This list of emails was likely sourced from other sites - probably Bitcoin related ones. Itís clear there was no data breach because no other user information is provided."
They have not addressed the claim that they cooperate with US authorities in the blog post, but a spokesperson has confirmed for ZDNet that they do work with them - with FinCEN especially - but that they are not under a gag order.
In the statement, the company also defended its "request money" and email address/user enumeration features, and added that they have implemented a number of things which make them less convenient for would-be spammers.
This was a direct response to a recent post by "information security enthusiast" Shubham Shah, in which he explained in detail how these features can easily be misused by spammers.
In the meantime, Coinbase users have taken to Reddit to complain about the phishing emails posing as legitimate Coinbase notifications they've been receiving, and I doubt they will be happy with that response.