Matrix team runs, Multiple decker questions Options

[WolfJack]

I did some, brief, checking through other threads and haven't seen this covered. I know that Matrix clearly states that multiple users in a system all get their own security tallies, Matrix p. 110, but I haven't found anything that deals with two or more deckers working co-operatively.

Example:
Decker A and Decker B log into an Orange host looking for paydata. Decker A handles all the Locate paydata operations while Decker B watches his back for IC. Decker A find the paydata but raises his security tally enough to set off a Blaster IC.

The question: Can Decker B see the Blaster IC, react to and attack the IC??

Also, for clarification, Decker B would have to make Null operation tests while in the host, yes? How often would he make a Null operation test; every time Decker A makes a test, every X rounds, every X minutes, whenever the GM feels like it?

Any help is greatly appreciated. If there are no set rules for the above, what are the majority of feelings from everyone?

-Wolf