Great, but vulnerable/buggy!

Although this plugin does what it says it does, it is vulnerable. I started a giveaway with 500 keys, and 400 of these keys were suddenly snatched by one person with the same IP address. Yes, I didn’t limit it to one IP address, but it should still be limited to one key per user ID.
I’m not sure if they were intentionally stolen or if it’s a bug with the plugin, but it’s making it unusable in its current condition.