The phrase refers to a "combo list"—a text file containing hundreds of thousands of stolen login credentials (email/username and password combinations) aggregated from multiple data breaches. These files are primary tools for credential stuffing attacks, where hackers use automated software to gain unauthorized access to accounts by exploiting the common habit of password reuse across different platforms. The "400k" Data Leak Context

: Attackers prioritize popular services like PayPal and Amazon because they hold financial value.

: Stolen contact info is used for targeted social engineering attacks. Actionable Steps for Protection

: Allegedly includes names, addresses, emails, phone numbers, and order histories.