I am very interested to know if cryptocurrency wallets like Bitcoin Core, NEON, Electrum can ever be hacked ?
There is no cryptocurrency wallet that is not hackable. It all depends on how well you can secure your wallets by taking all known security measures so as to protect your funds.
Indeed, we are right now living on digital world where people connected with internet. I am believe if the thing in digital form, it can be hacked. Hackers always improves their skill and knowledge, and we should be always aware with our crypto wallet. There is nothing wrong with always carefull