The Protonmail.de Leak Could Unlock Your Email and Everything Else

HEROIC analysts identified a combolist file circulating on Telegram named “protonmail.de - 17.570 emails.” The file surfaced on June 10, 2026 and contains 17,570 records pairing login credentials with plaintext passwords, along with the URLs of the sites each login was meant to unlock. The file targets the protonmail.de domain specifically, filtering out accounts on Proton's privacy-focused email service.

Why This Combolist Is Dangerous Despite the Provider

Even privacy-oriented email providers cannot protect an account if the password itself was captured elsewhere, whether through phishing, malware, or reuse from another breached site. 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 Even for Privacy-Conscious Users

Anyone who reused a Proton password on a less secure site elsewhere may find that convenience is exactly how this exposure happened. 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 Even Privacy-Focused Email Ends Up in Combolists

A combolist is not a hack in the traditional sense. It is a compiled text file, usually pairing an email address or username with a password, that criminals assemble from many smaller sources: old breached databases, phishing hauls, and stealer-malware output that has already circulated in underground channels. Combolists get repackaged, renamed, and re-uploaded constantly, which is why the same stolen credentials often resurface under a dozen different file names over time.

What makes combolists dangerous is not sophistication, it is scale and reuse. Attackers load a combolist into automated credential-stuffing software that tries each pair against banking sites, email providers, streaming services, and social platforms in seconds. Any password reused across accounts turns a single leaked line into several 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.