You can withdraw negative amount of money from SampleOffer.getDailyPayment() because the calculations ignores historical changes to dailyWithdrawLimit.
This fixes the issue slockit#171. Instread of remembering how much was payed out, it is remembered when the last payout was. Type type of withdraw limits has been also changed to uint128 to avoid overflow calculating the amount for the withdraw.
You can withdraw negative amount of money from
SampleOffer.getDailyPayment()because the calculations ignores historical changes todailyWithdrawLimit.