For the Star Trek: Picard novel, please see Firewall (novel).
A firewall was a computer safeguard that prohibited access to secure files.
(DIS: "The Wolf Inside")
(DIS: "An Obol for Charon")
Leland's Section 31 personnel file was guarded by a firewall which Philippa Georgiou was able to circumvent. (DIS: "Saints of Imperfection")
(DIS: "Perpetual Infinity")