They are rarely the result of a single hack. Instead, they are "credential stuffing" collections compiled from various historical data breaches. When a site like LinkedIn or MySpace is breached, those credentials eventually find their way into these aggregated text files. Why People Search for the 125K Combo List
Hackers use automated tools to "stuff" these combinations into the login pages of popular sites (like Netflix, Amazon, or banking portals) to see which ones work.
In the corners of the internet where data is traded like currency, you’ll often see headlines like or "Massive 125k Email/Pass Combo List Free." To a casual user or a budding security researcher, this might look like a treasure trove of data. To a cybercriminal, it’s a toolkit. But to the average person, these files represent a significant risk. What is a "Combo" File?