While hacking the terminals, I started to notice that the central database can be locked down to prevent anymore hacks related to it (after attempting prototype/schematic hack multiple times without success), but I never seem to notice the log stating that it's locked down until I started to look very carefully at those words.
So after I saw those words, they don't seem to stand out at all, blending with all the other brown-colored ones that aren't so important. I think they should have different color since they have an effect on gameplay (to remind myself not to keep spamming those database commands).
Also, the manual states: "
Successful indirect hacking of central "database-related" targets (queries, schematics, analysis, prototypes) incurs a 25% chance to trigger a database lockout, preventing indirect access to those types of targets at every terminal on the same map."
From what I experienced, it looks like unsuccessful indirect hacking can also incur database lockout.