In plain words
It is the outside view of a firm: domains, email settings, websites, forgotten systems and staff addresses in breach data, read without logging in to anything.
Why it matters to a firm
Most of what is found this way is simple to fix once someone knows it is there. LeakTrace reads the same outside view, and a person reviews every finding before the firm sees it.
How anyone can check it
List every domain your firm has registered, then look up each one’s mail records and check whether its website still runs.