Spiders are corporate hackers.
Higher end facilities will have their own dedicated spider or a team of spiders constantly patrolling the network searching for intruders or scanning for network vulnerabilities.
If a facility has been compromised by a team of shadowrunners; Spiders have been known to jump in to an entire facility thus preventing doors, lights, cameras, fire suppression, etc. from being able to be hacked. There are two ways to deal with a spider that has jumped in to a facility; the runner's hacker can engage the spider in cybercombat, or the runner's can cause enough physical damage to the facility to incapacitate the spider from deadly biofeedback.
- Unwired, 68-69