These lists are rarely from a single breach. Instead, they are "Compilation of Multiple Breaches" (COMB), where attackers aggregate data from many different leaks (e.g., social media, gaming sites, corporate databases) into one master file.
Cybercriminals use automated tools like OpenBullet to test these 12,000 combinations against hundreds of popular websites per minute. They rely on the fact that users often reuse the same password across multiple accounts. 12K COMBO LIST EMAIL PASS.txt
If you suspect your email might be in such a list, take these immediate steps: These lists are rarely from a single breach