What it is
Paste sites (Pastebin, Ghostbin, Anonfiles, Rentry, and their successors) get used by attackers to publicly stage credential dumps, mailing lists, and OSINT compilations.
Why it matters
A pretext-attack chain starts with a target list. Paste-site scraping produces a target list for free.
The check behind the finding
Check the address in a public breach-notification service, which also covers paste sites.
Closing it
This can be reduced, and it starts with knowing which addresses are listed and where. The assessment lists each address found and where it was listed, and gives the steps for each.