I have a some alt-coins in My Ether Wallet, and normally using personal key to open & close wallet...
And, Not using that much down & up load program and also, frequently updating virus program
I Know Using cold-wallet is most safe one, but is it really necessary to do that ?
Hacking the My Ether Wallet is occasionally happen ?
Some Dekstop Anti Virus can't detect Phishing websites as their main purpose it to protect your PC system and not your browsing experiences. But fortunately, there are browsers that contains built-in Phishing and Malware Protection such Mozilla Firefox and Google Chrome so I suggest to only used this browsers to accessed your MyEtherWallet.
But it doesn't mean you are 100% safe
because even how well protected your system is, if your actions is not responsible then you might be fall on a trap like accidentally sharing your private keys online or any relating to that.
Cold Wallet is not necessary at least in my own view but if you intend to hold long as in untouchable then I suggest to just buy hardware wallets like Trezor and Ledger. We don't need to be exaggerated in terms of the security on our own MEW as long as we know some basic safety precautions and knowledge about it.