I cannot overstate the importance of keeping your account keys secure. Specifically, you will never need your Owner Key/Master PW except for account recovery and you should never use anything more than your Posting Key unless you are absolutely sure the site is safe. It should go without saying that you are responsible for your own account security here.
You can tell that a post link is taking you away from https://steemit.com because when you hover over it for a couple of seconds, it will display the message shown at the bottom of this example:
RE: My acccount was hacked into and stolen from by @contestbuddy and @steem