VICE comes with built-in support for up to 4 teams, and the ability to fight on a private combat channel, albeit the default is for the player to fight independently, on the public channel. 

Team play operates in 2 different modes: with and without friendly-fire.  When friendly-fire is disabled, it is impossible to hurt teammates with bullet-type attacks or the melee attack; however, you can still damage teammates (and yourself) with bombs and kamikaze attacks.  When friendly fire is enabled, any type of attack can damage a teammate. 

In either mode, you gain 1 point for killing an person on another team (or somebody fighting independently) but lose 2 points when killing a teammate.

By default, friendly-fire is disabled.  Friendly fire is only available on private combat channels and is designated by private channels whose channel_password is preceded by "ff".  By this design, everybody on a player's combat channel will have the same friendly-fire settings.

Installation
Team and private channel based functions may be installed into any VICE unit by sending the appropriate link message to the VICE sensor. See below.
To install friendly fire functionality, "ff" must be affixed to the beginning of channel_password. This may be accomplished by creating a function that converts the channel_password key and combines it with "ff"+(string)channel_password, and then resends the "channel" link message. To restore, simply resend the "channel" link message with "channel_password", without "ff".

Link Message 
There are only 2 link messages for setting up teams and private channels of a VICE unit or target:  

 
Notes

• Unlike normal units, VICE targets cannot be damaged by teammates under any circumstances, including bomb attacks.  The reasoning behind this is to prevent griefing for team-based competitions, so that a griefing team member can't sabotage their team's progress by intentionally destroying the team's objects.