In escape part players have to escape laboratory.
First 3 escaped players will be awarded by additional frags and credits. 
Zombie mod begins after escape part. Alive players have to survive, and zombies have to infect alive players.
Zombies can use all types of melee weapons.
Infection can spread without zombie activityall servers use dproto so you can play from non-steam clients
To play on experimental zombie server you need to download additional resource pack.