When Jack (Jeremy Northam) wraps his handkerchief around Angela's (Sandra Bullock's) bare midriff, it borrows directly from the Alfred Hitchcock thriller Les enchaînés (1946), wherein Cary Grant does the same thing to Ingrid Bergman, cautioning her that without it, she might catch cold.
On the checklist on Angela's computer, it says "Bring 2600 Mag," and 2600 is a real hacker's magazine.
The game that Angela is playing/debugging at the beginning of the movie is the Apple version of Wolfenstein 3D (1992), similar to the console editions of the game released on the Atari Jaguar and 3DO.
One of the few PG-13 rated movies permitted to use the word "fuck" in a sexual context.
Angela's chatroom contact Cyberbob tells her about the "Praetorians," an Illuminati-esque group which, he states, has an affiliation with Wall Street. In reality, this is the name of an extremely private internet and corporate security company in Texas, whose customers actually do include Wall Street.