The ac.auone-net.jp Breach Gave Hackers 13,786 Working Logins

HEROIC analysts identified a combolist file circulating on Telegram named “ac.auone-net.jp - 13.786 emails.” The file surfaced on June 10, 2026 and contains 13,786 records pairing login credentials with plaintext passwords, along with the URLs of the sites each login was meant to unlock. The file is filtered to the ac.auone-net.jp domain, a webmail service, meaning the uploader specifically isolated accounts tied to that one provider.

Why a Domain-Specific Batch Like This Is Dangerous

Isolating credentials by a specific email domain lets an attacker focus a credential-stuffing run entirely on that provider's login page, improving their odds of success. Because every password in this file is stored in plaintext, anyone who downloads the list can read and use each credential immediately, with no cracking or decrypting required. Combined with the target URLs included in the file, an attacker does not need to guess where to try a stolen login. The file tells them exactly where to go.

What Was Exposed

• Email addresses tied to the accounts in this file, usable to identify and target victims directly.
• Plaintext passwords, stored and shared with no encryption, meaning anyone who obtains the file can read them instantly.
• URLs showing exactly which site or service each credential pair unlocks, making it trivial for an attacker to know where to try each login.

Why This Matters for That Email Provider's Users

Nearly 13,800 accounts tied to a single webmail domain gives an attacker a ready-made, focused target list. The core risk with any combolist is credential stuffing: automated tools that take every email and password pair and try it against dozens of popular websites in seconds. If you have ever reused a password across more than one account, and most people have, a single leaked line here can lead to a compromised email account, drained loyalty points, hijacked social media, or worse.

How Domain-Specific Webmail Combolists Are Built

A combolist is essentially a shopping list for account takeover. It combines usernames or email addresses with passwords collected from earlier breaches, phishing operations, or infected devices, then gets distributed through Telegram groups and dark web forums where buyers look for fresh or "validated" batches.

The real threat comes after the file changes hands. Attackers run combolists through automated credential-stuffing tools that test each pair across banking portals, email services, and online retailers. A single reused password can turn one leaked line into a chain of compromised accounts.

Check If You Are Affected

The safest move after any exposure like this is to find out quickly whether your own information is part of it. HEROIC's free breach scanner checks your email address against a database of more than 400 billion breached and leaked records, including combolists, stealer logs, and other underground dumps like this one. If a match turns up, change the affected password immediately, enable multi-factor authentication wherever it is offered, and avoid reusing that password anywhere else.