A combolist (short for "combination list") is a plain text file, typically formatted as email:password or user:pass . These lists are curated by aggregating data from multiple security breaches and info-stealer logs.

: Use tools like Have I Been Pwned to check if your email has appeared in a recent combolist dump. Credential Stuffing Tools and Techniques, Part 1 | F5 Labs

To protect your accounts, cybersecurity experts from organizations like OWASP recommend: