When the pool on the roof "springs a leak", you hear a sound effect for an "impact" type sprinkler. This is the type you would use on your lawn or garden with the little arm that slaps back and forth to move the head, and they have a very distinct sound due to the way they operate. Fire sprinklers have fixed spray heads with no moving parts, and can not make that noise.
Several scenes show the Met Life building (with "Met Life" in huge letters) behind Grand Central. However, the old stock "sky view" footage right before Dade's first day of school shows the building with its original "Pan Am" signage, which was taken down ten years before filming.
When Dade first enters Cyberdelia, there is an overview shot of the whole place, and for a moment we see Joey and Phreak on the top balcony talking around a table. The problem is, this is the scene from the next day. You can tell by the clothes they are wearing.
In the scene where all of the hackers watch "Hack the Planet" prior to this episode there is a newscast where Gill is being interviewed was clearly shot before this scene. He stands, acts and says exactly what he does in the next scene. You can also see Joey being walked down the stairs on the TV and in the film scene afterwards.
When Dade gets tricked into going to see the 'Pool' on the roof of the school, right after he walks out of the door, he turns back to the door and turns the door handle completely. In the next shot, he can barely wiggle it because it's locked.
We see Kate kissing Kurtis on the bike outside Cyberdelia. In the background we see, Crash, Phreak, and Joey walk up and stop. In the next shot, Crash and Phreak are in different positions and Joey is still walking up.
In English class, Kate is seen underlining her quote from her mother's book on the chalkboard. After the teacher reads Dade's quote, and Kate says that he is not supposed to be in this class. In the next couple of shots there is no underlining under her quote. Also the exclamation point at the end of the quote has black chalk used as shadowing, Kate is clearly only using white chalk.
In Cyberdelia, as Dade's score is appearing on the high score list, we see his score "crush" the fourth and third place scores on the high score list. The camera then shows him looking at his score while two more sounds of "crushing" occur. This should put him in first place, however, the camera then goes back to the high score screen where his score "crushes" the second and first place positions. Thus, the error occurs in the existence of the sound of "crushing" while the camera is not on the high score list.
In the "Hack the Gibson" scene Dade steps out of his phone booth to the one in front of him to answer Plague's call, which is the same booth occupied by Burn who is present before the phone rings, disappears during the call and then reappears again after.
In Cyberdelia, as Dade starts playing the video game after Libby moves out of the way, she stands behind Dade to his right. Yet, in the next scene when Curtis asks if Dade is bothering her, Libby is behind Dade to his left.
When Kate and Dade are walking beside the river on their date, you can clearly see Kate's intricate eyeliner/eye makeup. Yet when they are swimming in the pool before her head goes under and her face gets wet, it has all disappeared leaving just her eye shadow and no smears.
When Joey kisses Lucy (his computer) you see a number "1" sticker on the left side of the monitor, but when the monitor is confiscated by the Secret Service you see the number "1" sticker on the right side of the monitor.
Later, when Joey is shown being distraught over the disassembly of his computer, the number "1" sticker appears to be back on the left side of the monitor bezel.
When the Secret Service pushes Dade into his room you can see a blue shirt hanging on the back of his door. When Gill is dismissed from the room the shirt is no longer there. When the "Plague" is speaking to Dade the shirt reappears. When the "Plague" smashes Dade's stereo, the shirt disappears again.
In the scene when Acid is showing-off her laptop, they speak of the laptop having a processor called a P6 and a PCI bus. Further examination of this scene and another scene with them looking over the damaged code, the laptop that Acid-burn has is clearly a Macintosh Powerbook 280C (sub-notebook) made by Apple Computer Inc. This model does not have a PCI-bus, or a P6. It does have a Motorola 68030 33mhz CPU.
When Kate is describing the specs of her machine she says, "It's a P6 chip. Triple the speed of the Pentium". Dade then says, "Yeah. It's not just the chip, it has a PCI bus". Kate says, "Indeed. RISC architecture is gonna change everything". The P6 chip is a CISC design, not a RISC. Also, the Pentium has a PCI bus so there wouldn't be any reason to mention it.
The P6 processor, which was not yet released at the time of filming but which later came out under the name Pentium Pro, was only twice as fast as even the slowest Pentium processor, not 3 times as Kate claimed.
When Zerocool, freak, and Cereal killer first go to lord Nikon's apartment they are watching television which is showing the news and Agent Gill is talking about hackers in the background you see the FBI agents taking away a suspect behind them and it is clearly Joey. However this scene doesn't happen till the next morning after we see Joey in the shower and the FBI agents are in his bathroom and take him away. Then as they are taking Joey down the stairs Agent Gill begins to give the interview that the guys were watching on Nikon's TV the night before.
In the opening sequence, the plane is shown with the sun on it's left (port) side, meaning it was heading west. If it were heading from Seattle to New York City, the sun should be on it's right (starboard) side.
After Richard Gill's credit card is canceled by Dade, the scene cuts to the card being swiped through a machine by a waiter. The card is run through the reader "right side up", with the Mastercard logo at the bottom. The magnetic stripe is at the top of the card and could not have been read this way.
When Dade is introduced to Lord Nikon, he asks if anyone knows who the Hacker Acid Burn is, but no one knows. Later at Kate's party, the same hackers that said they did not know who Acid Burn is, are calling Kate "Burn" as though they were aware of her hacking handle. However, they are lying because they didn't know who was asking and they didn't want to reveal Kate's identity and get her into trouble.
When swimming in the rooftop pool at the end, Kate and Dade's ears are underwater as they talk to each other. They would still be able to hear each other speak, since water transmits sound waves just like air, albeit somewhat distorted to the human ear. Their voices would be audible to one another, just not as clear as if they were completely out of the water.
Hackers is set in NYC however in the "Hack the Gibson" scene Plague places a call to Dade in Grand Central Station but the phone rings using the European tone (ring ring - pause - ring ring) rather than the American tone (riiiiiing - pause - riiiiiing) indicating that this scene was either filmed or sound recorded in the UK.
In the opening scene of the plane flying Dade and his mother from Seattle to New York, the plane's tail clearly shows "757" on it, indicating this is likely Boeing stock footage of the plane (and not a commercial airline). Additionally, the cabin shot shows 2-by-2 seating, which is not accurate of the economy class plane seating configuration (which is 3-by-3) unless they are in first class. Based on appearances (narrow seats) and coordination with the described economic situation of the mother, them being seated in first class is highly unlikely. At the end when "Mr. Babbage" is flying to Japan, the plane shown is clearly a Boeing 727. The flight attendant tells him the flight time is about 14 hours. A 727's range is about 2700 miles, and cruises at about 615 mph. Simple math would tell you that a 14 hour flight was not feasible with this plane, which is logical since the plane was always considered a medium-range aircraft.
At school when Dade is looking at Kate's profile information to promote himself to Adv English, Dade's school photo is shown in the new window that is opened on the computer before Dade enters his name.
As Dade opens his soda while taking over the TV station with his computer, the viewer can see that the phone is on the hook, and Dade's modem (the box in front of the phone with two rubber acoustic couplers) is unused, yet proceeded to get into a "hacker battle royal" with Acid Burn.