Detects bursts of Google Workspace device registration events for the same user, where three or more distinct "google_workspace.device.id" values are emitted in a one-minute window. Although "DEVICE_REGISTER_UNREGISTER_EVENT" fires routinely on session/sync registration and is not a true physical device enrollment, legitimate user activity typically produces fewer than three distinct device IDs in a single minute. A high-cardinality burst is the fingerprint behavior of AiTM phishing-kit relays (Tycoon2FA Google variant, EvilGinx phishlets) and stolen-OAuth-token replay tooling, both of which mint a new session attestation per relay or replay attempt.

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Detects the first time a Google Workspace user is observed authenticating from a device of a given type (e.g., WINDOWS, MAC, ANDROID, IOS, LINUX) within a historical window. Note that "DEVICE_REGISTER_UNREGISTER_EVENT" events do not represent one-time physical device enrollments; the Google Reports API emits a fresh "google_workspace.device.id" on each event, and the same physical device may produce multiple events per day as sessions/sync renewals occur. The rule therefore surfaces a user authenticating from a new device type, not a new physical device. This is still high-fidelity because adversaries who compromise a Workspace identity via AiTM kits or stolen OAuth refresh tokens frequently relay sessions from device types that diverge from the legitimate user's baseline (e.g., a WINDOWS session appearing for a known macOS user, or simultaneous WINDOWS+MAC sessions within minutes), which is the canonical kit fingerprint. Because the underlying token retains access after password rotation, treat unexpected device-type divergence as a compromise indicator and revoke tokens, not just credentials.

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