Actually, it appears that the problem was caused by a third-party, to whom Microsoft outsourced the firmware for the 1st-generation Zunes. Looking over the source code that was used, the problem was that the check to see if it was a leap year left out a critical component: what to do if it was the 366th day of the year. Normally, on non-leap years, the code, when it hit the 366th day, would subtract 365 from the day counter and add one to the year counter. If it was a leap year, it would subtract 366 if the day counter was 367... But if it was 366? Oops, they forgot to handle that contingency. Hence, on midnight, December 31, they all crashed. (midnight as in as soon as it became New Year's Eve, NOT as soon as it became 2009) But when it became January 2nd, the Zunes were able to right themselves, as their day counter was thus 368, and so they wouldn't hit the infinite loop that locked them up.