My ETH funds were stolen and I am sure I didn't give out or handled carelessly the Mnemonic phrase, JSON file, private key nor the key store. Please I want to know ways by which a cryptocurrency wallet could be hacked.
usually weak security. main reasons are...
....obv a trogan virus or similar
.....a keylogger exploit
https://en.wikipedia.org/wiki/Keystroke_logging......your friend/work colleague pinched your passes (yes it happens)
.....fake ETH phishing site stealing your data (etherwallet does provide a warning on this regarding their site)
...the new c&p virus circulating the crypto world. (its unlikely this as your situations is different, however since you asked above i added this one.
https://techcrunch.com/2018/07/03/new-malware-highjacks-your-windows-clipboard-to-change-crypto-addresses/