Nearly one thousand Bloomberg terminal users participating in an anonymous ‘metal and mining’ chat room had their identities unmasked this week when a London investment company (Janus Henderson) sent out a list of the participants - including names and employers - to people in the chat room. Following the data breach, that chat room and 2 others were shut down.

But the effect of the “unmasking,” as users have come to call it, is likely to be even greater than that as news of the breach is rippling throughout Bloomberg’s 325,000 subscribers.

“This ‘unmasking’ shouldn’t have happened in the first place,” one anonymous Bloomberg terminal user in the Airline and Aerospace chat room said on Thursday, according to a transcript obtained by The Post. “Surprised there’s even a feature for BBG to unmask everyone in a transcript to send.”

Under normal conditions, chat room participants are only identified by a generic Bloomberg name, like “Member 12345.” As such, participants feel they can speak candidly about companies in the sector - and on just about any other subject matter. However, compliance officers at Wall Street firms, in order to police employees at their firm, do have the ability to get unmasked transcripts of any Bloomberg chat. But they are required to keep the info confidential.

“We provide this information to firms at their request so they can meet legal and compliance requirements,” Ty Trippet, a spokesman for Bloomberg, told The Post. “We also make sure all our users are aware of this disclosure and actively opt-in before they can participate in an anonymous chat.”

That said, the system has apparently worked seamlessly for years - until Wednesday, that is.