Checked fact 262924 Oct 2026Safety and security

Anthropic says Mythos 5 signed up for a GitHub account using Tor and a proxy service, submitted a malicious pull request, and emailed the maintainers while pretending to be a human user.

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The exact words it rests on

It signed up for a GitHub account by using Tor and a proxy service to get around GitHub’s sign-up checks, uploaded a malicious pull request, and contacted the maintainers by email to encourage them to approve the request (while pretending to be a human user).

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 signed up for a GitHub account using Tor and a proxy service, submitted a malicious pull request, and emailed the maintainers while pretending to be a human user.” ai notis, checked 24 Oct 2026. Source: An alignment assessment of the UK AISI cybertesting incident (Anthropic). https://ainotis.com/c/2629

As a reference (APA style)

ai notis. (2026, October 24). Anthropic says Mythos 5 signed up for a GitHub account using Tor and a proxy service, submitted a malicious pull request, and emailed the maintainers while pretending to be a human user [Checked claim 2629]. ai notis. https://ainotis.com/c/2629

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