Because the original deployments of IDS were just passive data collectors there was no impact on network performance from adding new signatures so the data base grew and grew and the logs IDS generated grew and grew to the point where even a mid-size organization would receive millions of alerts a day.

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They're also used widely in cellular base stations, Internet routers and high-performance data-networking switches.

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The telemetry used in civil aviation transmits data on engine performance and the behaviour of other systems back to base while the plane is in the air.

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