User blog comment:Argorrath/Treyarch posts a message of zombies; possibly hinting to a DLC 4/@comment-173.55.118.141-20130802214339/@comment-3123696-20130802220138

12+43=53

53-20=33

The third note is made the 19th of November. November is the 11th month of the year.

33/11=3

HALF LIFE 3 CONFIRMED