ETF flow is the net money moving into or out of an exchange-traded fund. In practice, it is measured through creations and redemptions: when investors buy shares and new units are issued, the flow is positive; when shares are sold back and units are redeemed, the flow is negative. It is a simple but powerful signal of demand.
In cyber security and market surveillance, ETF flow matters because it helps defenders separate genuine buying from short-lived price spikes driven by leverage, bots, or forced liquidations. Strong positive flows can support a rally and suggest real capital is entering the market, while weak or negative flows can warn that momentum may fade. Monitoring abnormal flow changes also helps trading platforms and risk teams spot suspicious activity, operational stress, or account compromise that could distort market behavior.