Using malware (Infostealers) that grabs passwords saved in a user's browser [6, 7]. Security Recommendations If you suspect your information is on such a list:
Taking data from a leaked site (e.g., a gaming forum) and "checking" it against mail providers.
Use services like Have I Been Pwned to see if your email has appeared in recent leaks.
Using the verified accounts to send spam or phishing emails to the victim's contact list, as these emails are less likely to be flagged by spam filters since they come from a legitimate address [3, 4].
Immediately change passwords for your email and any account that shared that password.
Harvesting personal information, tax documents, or private communications found within the inbox [2, 5]. How These Lists Are Created