A security breach is any incident that results in unauthorized access of data, applications, services, networks, and/or devices by bypassing their underlying security mechanisms.

Hackers are known to visit https://databases.today and https://haveibeenpwned.com. These websites have an archive of breached data. The following screenshot provides the view of the databases.today website:

To harvest more information about the target, pentesters would typically look into websites such as zone-h.com to provide information about breaches to it. For example, defacement of sidehustlewarrior.com was performed by an underground group named Bangladesh Grey Hat Hackers. The following screenshot provides details on the IP address, web server, and operating system used during the defacement: