That's kind of a perverse incentive to be less careful at first and cash in later

As predicted by Scott Adams some twentythree years ago :-)

http://dilbert.com/strip/1995-11-13

Anyone who has ever placed in the underhanded C contest should be automatically disqualified from committing code. You know, "your hands are deadly weapons" type of exception. \s

Nah, you just review what they submit like everyone else. If you block them, they'll do the contest under an alias or use different names for contributions. Plus, they're really smart folks who might bring a lot of value to the project.

Sure, they put them intentionally there :)

for 500k they might as well. It's an ugly practice.