If you see "This dApp could be malicious. Do not proceed unless you are certain it is safe." when confirming a transaction, Phantom may prevent you from completing the interaction. This warning appears when Phantom can't accurately simulate a transaction before it's sent.
Transaction simulation lets you preview what will happen when you confirm a transaction. If Phantom can't simulate it accurately due to dynamic or non-standard behaviors, it can't provide the usual level of protection and shows this warning instead.
For users
Be cautious when continuing with any transaction that displays this warning. Only proceed if you fully trust the app and understand the risks. If you're unsure, pause and learn more about the app before proceeding.
For developers
If you're the developer of the app and want to understand why this warning appears or how to prevent it, see Domain and transaction warnings in the Phantom developer docs.