Offer your thoughts or opinion on the input financial query or topic using your financial background.

MasterCard won't disclose who leaked my credit card details
Others have already commented on the impact of anything which dissuades merchants from raising possible breaches, so I won't dwell on that. Maybe we need stronger legislation, maybe we don't, but it doesn't change today's answer. Often it works the other way around to what you might expect - rather than the merchant noticing and notifying Visa/MC/others, Visa/MC/others spot patterns of suspicious activity (example 1). I don't have any data on the relative numbers of who is being notified/notifying between merchants and payment processors, but at the point when your card is identified as compromised there's no reason to suppose that an individual merchant in the traditional sense has been compromised, let alone identified. In fact because there's a fast moving investigation it could even be a false alarm that led to your card getting cancelled. Conversely it could be a hugely complex multinational investigation which would be jeopardised. It's simply not safe to assume that simply "brand X" has been compromised, therefore everything "brand X" knows about you is also compromised: Furthermore there's no reason to assume the merchant has even admitted to, or discovered the root cause. MC/Visa/Banks, at the point at which they're cancelling cards simply can't say (at least not in a way that might expensively backfire involving lots of lawyers) because the standard of proof needed to go on record blaming someone is simply not yet met. So: yes it's common that you aren't told anything for all of the above reasons. And of course if you really want to find out more you may have some success with your local data protection legislation and formally make a subject access request (or local equivalent) to see what that brings back. Be sure to do it in writing, to the official address of both mastercard and your bank.