What features in ehtereum would ensure that the Dapp would never spy on you or steal your data?
closed as too broad by user19510, shane, flygoing, Ismael, Achala Dissanayake May 19 at 3:29
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The system is optimized for transparency it is required that all nodes can see all data and contracts in order to process all transactions and reach their own, independent conclusions about the world state.
There are design patterns for protecting confidential information in light of this structure. For example, don't put anything on the chain that you don't want disclosed. Use the chain to validate authenticity of documents by storing the hash of documents on the chain while keeping the details off-chain and disclosed on a need-to-know basis.
There are also private chain solutions with private transactions, contracts and states. Examples include Quorum and Pantheon, both based on Ethereum but refactored for enterprise settings. You could also look at Hyperledger Sawtooth which supports the EVM (and Solidity contracts). These private chain options provide privacy as well as enhanced consensus options for performance and finality in settings where the node owners are known and (mostly) trust each other.
Hope it helps.