These are usually stored as plain text files ( .txt ), allowing attackers to easily run automated scripts to test the credentials.

Files like this are rarely the result of a single hack. Instead, they are often or compilations:

A "full mailaccess" file specifically targets email accounts, which are "goldmines" for identity theft because they serve as the recovery hub for most other online services.

Hackers collect stolen login details from thousands of smaller breaches and merge them into massive databases.