I heard that using a simple non-custodial wallet like Electrum on your system may be less secure but if we combine it with Multi-Sig, it would be impossible for the hacker to get hold of our funds even if he manages to hack the system Is it true?
If your multi-sig is set up online, or in a single device, it defeats the purpose of a multi-sig wallet and hackers can compromise your wallet and steal your funds. Also if you don't have a proper backup of your seed phrases and master public keys, you can either lock yourself out of your funds or lose the funds easily if your backup is compromised.
Let's say you want to set up a 2-of-3 multi-sig wallet, for strong security it should be stored in a hardware wallet, airgapped device and maybe an online wallet. Take note that in a multi-sig set up you need all your master pub keys to recover your wallet, so this is a great way to back it up:
- Seed phrase 1 and Master public key 2
- Seed phrase 2 and Master public key 3
- Seed phrase 3 and Master public key 1
So if you lose one back up, you can still recover the wallet, and if an attacker compromises one backup, they can't spend the funds because they have just one key and you'll be able to move your funds to a safe wallet. Setting up a multi-sig wallet is kind of complicated, and if you don't know what you are doing, you may want to get a hardware wallet and add a passphrase to it as an extra layer of protection.