Yahoo Users Targeted in the 400K Yahoo Base Leak: 392,653 Logins

HEROIC analysts found a stealer log file named 400K Yahoo Base uploaded by a Telegram user in April 2023. The file contains 392,653 records taken directly from infected devices, targeting Yahoo account holders specifically, including email addresses, plaintext passwords, and the URLs those logins belong to.

Why This Is Dangerous

This file is built around one specific target: people who use Yahoo. It was not stolen from Yahoo's own servers, it was captured by malware sitting on victims' personal computers, which recorded their Yahoo login the moment it was typed or saved in the browser. Because the password is stored in plain, readable text, an attacker can log into a Yahoo account immediately, no cracking required.

What Was Exposed

• Email addresses
• Plaintext passwords
• URLs tied to each Yahoo login

Why This Matters

Almost 400,000 Yahoo accounts in a single file gives attackers a focused, high-value target list. Yahoo Mail often connects to banking alerts, password resets, and other online accounts, so a compromised inbox can quickly turn into a much bigger problem through credential stuffing and account takeover. Anyone who reused their Yahoo password elsewhere is also exposing every other account tied to it, opening the door to financial fraud and identity theft.

How Stealer Logs Work

Stealer log malware typically spreads through pirated software, fake email attachments, or malicious downloads disguised as something harmless. Once it infects a device, it quietly copies saved passwords and autofill data straight out of the browser and compiles them into a text file. That file, like this 400K Yahoo Base dump, is then organized by target and sold or shared on Telegram channels and dark web forums. Because the data comes directly from the browser, it tends to be accurate and immediately usable.

Check If You Are Affected

If you use Yahoo Mail, it is worth checking whether your login is part of this leak. HEROIC's free breach scanner searches a database of more than 400 billion leaked records and tells you instantly if your email has been exposed. Run a free scan today and update your Yahoo password along with any accounts that share it.