It wasn’t truly a “hack” so there’s still no technical security vulnerabilities to worry about at the moment. It is a rash of “phishing” scams Steemit has been seeing. The user was tricked into giving his password to someone posing as “Steemit security.” So don’t worry too much about logging in. But best practices are still to only go to Steemit through a valid bookmark you’ve created so as not to be fooled by a duplicate site an external link may direct you to, and log in with your posting key. Only use owner/master keys when dealing with funds & account management.