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eSteem apps are opensource and anyone can hold us accountable if source code of app is not treating private keys securely. We have PIN code feature that will encrypt your private keys on your device and only uses private key when signing transaction from your device on your device. As Luke mentioned we have added Steemconnect if you feel that is more secure. Please reach out to us if you have any suggestions or feedback on improving Surfer or Mobile. Thank you!
PS. Stay tuned for eSteem Mobile v2 release in few days!

Best esteem is the best steemit alternative outthere. you guys have been working very hard to help the community own the steem blockchain and not always relying on steemit.

Definitely good to be cautious. I’ve followed the eSteem dev team for a while, and I think they are doing good work. You can also log in to the eSteem surfer app using Steem Connect. Only ever log in with your posting key to keep your funds secure.