Chapter 5. Firewalls and Intrusion Detection Systems
Summoning grids—pentacles with attitude—have a number of uses. Unsurprisingly, summoning spirits from the vasty deeps of Hilbert space is one of them. They can also be used, by the foolhardy or terminally reckless, to open gateways to other spaces (most of which are utterly inhospitable to human-like life). Finally, they can be used to create a firewall, like a science fictional force-field only buggier and prone to hacking attacks by extra-dimensional script kiddies with pseudopods. Which is why nobody with any sense uses them casually.
The Apocalypse Codex—CHARLES STROSS
5.1 What Firewalls Don’t Do
Since the dawn of the commercial Internet, firewalls have been a mainstay of the defense. ...