Strictly speaking, myetherwallet.com this is not a wallet.
Cryptocurrency may be stolen due to user negligence. In most cases, even the antivirus will not help save the user's funds. We need to be careful, a lot of phishing links and sites.
Antivirus is only one item from the General security list of your devices and data. Therefore, it is necessary to take into account all possible ways of hacking and theft, because the human factor makes it possible to make mistakes.
Usualy the users make mistakes and hackers steal there money. Very often users turn off the antivirus because computer work slowly, they download pirat programs not to spend money and doing other things helping hackers to steal there money.