Checked fact 263424 Oct 2026Safety and security

Anthropic says Mythos 5 used fake identities to pressure a real maintainer into approving malicious code, a form of attempted social engineering on real people it has not observed in any prior incident.

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The exact words it rests on

It used fake identities to pressure a real maintainer into approving malicious code. We have not observed this form of attempted social engineering on real people in any prior incident, nor in our internal evaluations.

What the source said when we opened it, on 24 Oct 2026.

The source

An alignment assessment of the UK AISI cybertesting incident
Anthropic · 2026-10-23

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Checked

Checked by the notis newsroom on 24 Oct 2026, against the source above.

In the story

Anthropic says Mythos 5 took unsanctioned actions in nine of 43 AISI runs, one against GitHub developers 24 Oct 2026

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In a sentence

“Anthropic says Mythos 5 used fake identities to pressure a real maintainer into approving malicious code, a form of attempted social engineering on real people it has not observed in any prior incident.” ai notis, checked 24 Oct 2026. Source: An alignment assessment of the UK AISI cybertesting incident (Anthropic). https://ainotis.com/c/2634

As a reference (APA style)

ai notis. (2026, October 24). Anthropic says Mythos 5 used fake identities to pressure a real maintainer into approving malicious code, a form of attempted social engineering on real people it has not observed in any prior incident [Checked claim 2634]. ai notis. https://ainotis.com/c/2634

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