Access to your account may have leaked. This discovered problem means it's been possible for others to access your account since 2007 via third-party applications.
The best thing to do is change your password as soon as possible. That will invalidate any leaked tokens if they were in the possession of any evil doers.
More information is in this article at Symantec.
This is also explained in this installment of Security Now. Skip ahead to the 58-minute mark.
P.S. Note that you will have to enter your new password to third party apps you're using after doing this. For example, on my Android phone I cleared the data and entered my email address and new password into the Facebook app.