Der Spiegel report some of those in the Signal chat had publicly listed email addresses and mobile numbers with associated WhatsApp and Signal accounts, and publicly available passwords from prior breaches.
https://www.spiegel.de/international/world/pete-hegseth-mike-waltz-tulsi-gabbard-private-data-and-passwords-of-senior-u-s-security-officials-found-online-a-14221f90-e5c2-48e5-bc63-10b705521fb7
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