Most dividend trackers require you to create an account before you can enter a single holding. That account means your portfolio — the tickers you own, how many shares, and when you bought them — lives on their server. You're trusting a third-party company with a detailed map of your investment positions.
Some go further and ask to link your brokerage account directly, storing OAuth tokens that can read your full transaction history. If that company is breached, acquired, or shuts down, your data is at risk.
Elite Dividend Tracker stores everything locally on your device. The web app uses your browser's local storage. The iOS app stores data on-device. Nothing is sent to any external server for the purpose of storing your portfolio. You can use a full-featured dividend tracker without handing your investment data to anyone.