depending on the script.
usualy not, as the programs do crsah from time to time. (particulary if you edit access log and wirte there something about memory error or something like this). Each node is probably patrolled by agent from time to time to check if all the programs are up and running, but the Grid is one hell of a network, so this might be quite large time frame before spider gets notified.
blocking all comms is not function of this node (this ones provide services for cars drivign over the streets)
the communication node that provide matrix service, might be more difficult to hack (as it has a signal greater range and is a better hardware overall), plus there are multiple matrix service providers in Denver. (just like currect cell phones providers). and you'd need to hack them all to block matrix access to all 'links in range.
creating backdoor - unwired, pg. 97
Creating a reusable exploit requires a
successful Extended Software + Exploit (Firewall + System, 1
Initiative Pass) Test if you have at least security-level access on the
node—otherwise replace Software with Hacking. Once created,
this provides a hidden exploit that gives the hacker a +6 dice pool
modifier to gain access to that node using the Exploit program.
creating hidden account
A hacker who has hacked the node may also create a “legit”
account on the system (see Hackers & Editing, p. 225, SR4) and
then hide the fact that they created it. This requires a successful
Software + Editing Test if you have at least security privileges on
the node, or a Hacking + Edit (2) Test if you do not. For securitylevel
access, increase the threshold to 3; for admin access, increase
it to 4.
...
A hidden account is not visible to spiders or administrators,
being discernible only by the system.
...
To create a hidden account, you must already have access to
the node (either legit or hacked) and must follow the procedure
for creating a legitimate account noted above. On the next action,
the legitimate account must then be hidden with a Hacking +
Stealth (Firewall, 10 minutes) Extended Test.