Just tried the step suggested by these guys.
Well, the security questions are really dumb! I entered an e-mail address of a friend and entered the birthday. Then I was ask: what is your hometown? WTF everybody knows this guy's hometown!I didn't go any further but it made me very worried about my security questions. I'd better enter some password like stuff in the answer fields.
Then set up 2-factor authentication. There will no longer exist any security questions for your account. Problem solved.