The financial service industry has become the latest victim of this year’s surge in attacks against corporate targets after Experian plc saw hackers steal personal information belonging to 15 million Americans from its network last month. The plunder includes names, addresses, dates of birth and Social Security numbers along with detailed financial activity records.

The massive scope of the data leak stands in contrast to the breach itself, which the firm claims only affected a single server in one of its business-facing divisions that performs credit checks on behalf of T-Mobile International AG’s U.S. business. An internal investigation has narrowed down the affected group to subscribers who applied for postpaid services and device financing from the carrier in the two years through September 16.

That’s not nearly as bad as it could have been. As one of the world’s largest providers of credit information, Experian maintains records on some 600 million consumers and another 60 million businesses on top of that, which its investigation found to have skirted the attack. But that’s not much consolation for the millions of T-Mobile subscribers whose personal information may now very likely end up on the black market.

The firm is offering affected individuals two years of free credit monitoring and identity verification services in the way of damage control, but that won’t do much to mitigate the legal downfall if the breach is found to have occurred due to inadequate security or governance policies. Target Inc. failed to heed warnings about the safety of its point-of-sale systems in the run-up to its infamous 2013 breach and is still paying the price to this very day.

Experian faces many of the same risks. But until the investigation into the breach is over, we can only speculate about the specifics based on the few details that have been made available so far, like the fact that the company seemingly took a full three weeks to publicly report the breach.

Image via JavadR