There was a problem over Christmas with Valve's customers information being displayed on the steam store, but only from those who used the store that day, it also only affected a very small percentage of their user base. Considering it affected something like 30,000 people, and their user base is in the millions, relatively small.
In terms of your own account getting hacked, that is, partly, your own fault. You should take advantage of all the features Steam give you to protect your account, such as the mobile authenticator built into their mobile app. No one can log into my steam without access to my phone, even then, they'd have to crack my secure password. You also have the Family View feature, which, once setup, can prevent users from accessing certain features, such as the store.
You cannot blame steam alone for your account getting hacked, they do provide features to help eliminate this, but you yourself have to take advantage of them if you wish to protect your account.
Just wanted to reply here with this, just in case others read this and are put off using steam, the platform is secure, as long as you help keep it secure, by using the features they provide for you.
