That's a good question and I have two sites, one using Joomla or another one using Wordpress and I used to wonder how safe they were.
I think that any site is hackable depending on the hacker's skill level.
I don't have any confidential data on my websites and I create backups regularly. So if it ever gets hacked, I can reinstall my files and put the website back up and change my password again.
It costs money to secure a website. Go to
www.ssl.com and you will find some good options.
If you are storing any confidential information on your website, like customer database, credit cards etc., then you should secure it, otherwise just create regular backups.
JM2C