On the surface of Trialas IV, where Soong raised the Augments, there was a large device composed of two long glowing red tubes. This device has been seen in many places on TNG, DS9, and VOY, including, most interestingly, in Doctor Noonian Soong's lab in TNG: "Datalore". It is also seen in the control room of Cold Station 12, but with blue lights rather than red. The device was first seen in Star Trek II: The Wrath of Khan on the space laboratory Regula I. Aside from the Star Trek franchise, the device was also featured in Airplane II: The Sequel, where it was seen on the lunar base commanded by William Shatner's character, Buck Murdock.
At one point, it is said that there are a few hundred thousand possible combinations for the hexadecimal password. However, when Lucas finally reveals it, we see on the screen that it is composed of 16 characters, meaning that there were in fact about 18,446,744,073,709,551,616 (about 18.4 quintillion) possibilities.
The lethal diseases mentioned as being stored in Cold Station 12 in this episode are references to various (fictional) diseases which have been mentioned on previous Star Trek series, including xenopolycythemia, Anchilles fever, synthococcus novae type A, Rigelian fever, and Telurian plague.
When this episode was aired in the United Kingdom, broadcaster Channel 4 edited out some of the more violent scenes, including the part where Doctor Lucas gets tortured, and the close-up of the scientist being killed by the virus.
The trivia item below may give away important plot points.
When Persis arrives on Cold Station 12 and defeats the guards, they are all wearing the red piped Starfleet uniforms (aka Red Shirts), thus continuing the Star Trek trend of Red Shirts being killed or defeated to show off the villain(s) strength and to heighten the danger.