Maybe a better/simple idea would be give one simple code with just one bug. So the first one to see it win.
We have to found the good formula about the code/bug.
The main problem I see on this approach is that you must define a GMT time to start the contest, to everyone start at the same moment.
Not necessarily, we can do that by pm. Participant have to subscribe and fix a date/time. At this date/time they receive the code by pm and we see how much time it takes to receive the answer.