Identity thieves stole tax and salary data from big-three credit bureau Equifax Inc...
thieves were able to access W-2 data merely by entering at Equifax’s [W2Express] portal the employee’s default PIN code, which was nothing more than the last four digits of the employee’s Social Security number and their four-digit birth year.
http://krebsonsecurity.com/2016/05/crooks-grab-w-2s-from-credit-bureau-equifax/