I wonder how was that possible. The blog doesn't say much about that.
It is a security issue, and if your upvoting system can be compromised then other systems are in danger as well. I'm not judging, it's just basic IT security problem and I wonder how you plan to solve it.
@heimindanger the posting key is enough to give upvotes, which is the lowest rank but still, it is their responsibility to keep it safe.