The Zombie Apocalypse is upon us!

The Halloween Even is the same as Ice Season and it suppose to start earlier today but it had been postponed to tomorrow afternoon(PDT/PST Time)
Here is a Full Reprint from Mafia Wars Blog:

[UPDATE 2011-10-25 12:55pm PDT: This has been postponed to begin tomorrow afternoon, October 26th.]

Mobsters!

It's time to put your fighting skills to the test in a battle for humanity. For approximately 1.5 weeks beginning tomorrow afternoon, October 26th, fight as either a Survivor fending off Zombies or as a Zombie trying to turn Survivors into more of your kind in the Mafia Wars Zombie Apocalypse Fight Event!

Collect Ices Just Like Ice Seasons, But Otherwise Different

• • Instead of a 1-2 week "season," multiple zombie "waves" will occur until the event ends approximately 1.5 weeks after it begins. Each wave ends when the Zombie plague has overtaken the vast majority (~90%) of the population, which should occur multiple times by November 4th. The exact number of zombie waves that will occur isn't certain, however, as each could take anywhere from a few minutes to a few hours, depending on the number of people icing at any given time.
• • At the beginning of each wave, you are assigned the role of Survivor or Zombie and your role is visible to all as an icon next to your name in fight lists. The color of your pop-up windows' borders will remind you of your current role, which will switch at the beginning of each new wave. If you are a Survivor, there is also a chance that you will be turned into a Zombie any time you are iced. In the event that you are turned into a Zombie mid-wave, the ices/points accumulated while you were a Survivor continue to count toward mastering that wave. The item you can receive at the end of each wave is based on your role at the time the wave ends.

Each Role's Goal + How to Maximize Your Score
The goal as a Zombie is to convert Survivors to Zombies by icing them. The goal as a Survivor is to stave off the Zombie Apocalypse by icing Zombies while keeping yourself alive. To help you accomplish this, Zombie Protection and Antidotes will be available for purchase on the fight page and on select pop-ups. While your score will increase for each person you ice during this event, you will receive bonus points for icing players on the opposing side.

Zombie Apocalypse Fight Event Loot
There are many opportunities, depending on your score, to collect loot drop and mastery items for both sides. Collect enough ices to master all 4 of the tiers as a Survivor to earn the Ruby level Apocalypse Bike (125/85), and collect enough ices to master all 4 of the tiers as a Zombie to earn the Ruby level Brain Cage (76/117). The item you can receive at the end of each wave is based on your role at the time the wave ends.

Remember to keep your brain with you at all times,
The Mafia Wars Team