The "hacking"-sequences - the scenes where you see the "inside" of a computer - are mostly motion-controlled models, because director Iain Softley thought that actual computer graphics would look too artificial.
Jonny Lee Miller and Angelina Jolie were married shortly after the making of the film, and then were divorced four years later.
The cast were given three weeks to hang out together, get to know each other better and learn how to Rollerblade properly before filming began. They also spent most of that time studying computers and hacking.
The computer they break into is a fictional mainframe computer called a "Gibson" - a homage to cyberpunk author William Gibson.