Many online services have leaked usernames and passwords. Attackers can download databases of usernames and passwords and use them to access people’s accounts. Many people reuse their password for several services, and a leak by one site can give attackers everything they need to sign in to other accounts.
Cybercriminals trade and exchange stolen credentials from individuals and businesses on dark web forums and marketplaces. For example, criminals use stolen credentials to hack into online services and then exploit the victim’s personal information for fraud.