Kayo.moe Credential Stuffing List Data Breach (2018): What Was Exposed & What To Do

What happened

In September 2018, a collection of almost 42 million email address and plain-text password pairs was uploaded to the anonymous file-sharing service kayo.moe. The operator of the service contacted Have I Been Pwned to report the data. Further review determined that the material constituted a credential-stuffing list rather than the direct result of a single compromise of one organisation.

The incident was reported publicly on 11 September 2018 and is recorded as affecting 41.8 million individuals. No additional details on the origin of the individual records or the precise timing of their collection have been disclosed.

How a breach like this happens

Credential-stuffing lists are typically assembled by combining username and password pairs that have appeared in earlier data incidents. The resulting compilations are then distributed through file-sharing services that permit anonymous uploads. Once hosted on such platforms, the lists become accessible to anyone who obtains the link, enabling repeated automated login attempts against other websites.

Because the lists aggregate material from multiple prior events, the exact source of any individual record is often impossible to trace without further investigation by the organisations originally affected.

About Kayo.moe Credential Stuffing List

Kayo.moe operated as an anonymous file-sharing service that allowed users to upload and distribute files without requiring identification. Services of this type are used for a wide range of purposes, including the exchange of large data sets. When a substantial collection of login credentials is placed on such a platform, the exposure extends beyond any single company and can affect account holders across many unrelated services.

What data was at risk

The facts name email addresses and passwords in plain text as the data types present in the uploaded collection. Organisations that maintain user accounts commonly store these two fields together. The precise scope of any additional fields that may have accompanied the records remains undisclosed.

Why it matters

Plain-text passwords combined with email addresses allow straightforward testing against other online services. Individuals who reused the same credentials across multiple sites therefore faced an elevated chance that automated attempts would succeed on accounts not directly connected to the original source of the list. For the organisations whose users appear in such compilations, the incident increases the volume of suspicious login activity that must be monitored and mitigated.

If your data was in this breach

Review any accounts that use the affected email address and change passwords where the same combination appears elsewhere. Enable multi-factor authentication on important services to reduce the value of a password alone. A free exposure scan of the email address against known breach data can indicate whether the credentials have surfaced in other public records.

AICompiled with AI assistance from public sources and published under our editorial standards.