It's always possible 🤷 there are services that exist to help safeguard your private key like Amber.

GitHub

GitHub - greenart7c3/Amber

Contribute to greenart7c3/Amber development by creating an account on GitHub.

FYI I say it's possible, but they are themselves trusted applications and devs. Possible the same way it's possible for Amazon to get hacked and compromise your credit card.

i wouldn't go and stick my private key into any and all applications. some are more trusted than others. if you use Android, i would recommend using an application called Amber. it's a private key manager. it holds your key for you so that you don't have to give it to applications. sadly nothing like this exists on iOS. if you use a laptop or desktop, you can use a lot of nostr apps on the web and use a web browser extension to hold your private key and sign into apps that way. it's more secure than entering your key. check out

Explore Nostr Apps

to see what else is offered. i use an extension called Nostr Connect.

Derek isnt NOSTORE the one for iOS?