These lists are often compiled from multiple data breaches or via "stealer" malware.

Immediately update passwords for sensitive accounts, ensuring you use a unique password for every site. 300k UHQ.txt

Use services like Have I Been Pwned to see if your email has been part of a known breach. These lists are often compiled from multiple data

Using these credentials to access accounts you do not own is illegal under most computer crime laws, such as the CFAA in the US. 300k UHQ.txt

Use a reputable password manager to generate and store complex, unique passwords.