Visible crew/equipment: When Dr. Okun is about to unlock "the vault", and says, "The freak show," a crewmember wearing a black and white striped shirt is hiding under the vault's floor, right behind Okun. (Only visible on fullscreen DVD.)
Continuity mistake: When General Grey tells the President not to engage until they have visual, in the President's close-up the exterior of this F/A-18 Hornet is quite different than what was shown in the earlier shot, as the canopy closed over him. All the rivets around the canopy have disappeared and the 'danger' triangle is much closer to the name Patrick, the seat differs, etc. Plus the fact that the canopy and hull are actually one unit in the second shot. (02:02:15 - 02:03:15)
Continuity mistake: David calls Connie at the White House and she walks toward the divided pane windows, then pulls one curtain to the side. In the exterior shot facing her, the pane's white grille is between the two sides of the curtain, but in the next interior shot looking out, there's only clear glass, though we should see the grille, just as we see both sides of the curtain with her hand holding the right side. Then, in the next exterior shot facing her, it's back to the original with the visible white grille. (00:38:25)
Visible crew/equipment: When David reaches Connie on her cell phone in the White House, as she walks away away from the wall to head towards the window, a crew member (complete with water bottle and utility belt) can be seen on the lower left portion of the screen, before he quickly scrambles away. (Only visible on VHS and fullscreen DVD.) (00:38:27)
Continuity mistake: When David is looking for ice, the fridge door shelves are full of food. When Connie puts the bottle into the fridge, the door shelves are virtually empty. (01:24:55)
Visible crew/equipment: When President Whitmore returns to the containment lab to see the live alien, just as Major Mitchell and a Secret Service Agent walk to face the smoke filled lab, the actor's mark is visible on the ground as the Agent steps up to it. (Only visible on fullscreen DVD.)
Visible crew/equipment: After Dr. Okun unlocks "the vault" he explains the aliens' telepathic ability, and as David steps closer to the tanks the actors' marks are visible on the floor. (Only visible on fullscreen DVD.)
Visible crew/equipment: When Dr. Okun leads President Whitmore, General Grey, David and the rest to see, as he put it, "The big tamale," the red actor's mark is visible at the top of the landing as they all walk up the ramp. (Only visible on fullscreen DVD.)
Visible crew/equipment: In the containment lab, when the alien awakens and begins its attack, the alien moves from right to left towards a doctor, who is backed up against a door. The crewmember who is wearing the alien costume has on a white shirt and black trousers, and the costume's straps attached to the pants are visible, as well as some wiring at the back. (Only visible on fullscreen DVD.)
Revealing mistake: When the huge alien ship settles over the White House there is an exterior wideshot of the grounds. At the bottom of this shot it's funny how there are many tourists - adults and children, just milling around in front of the gate and across the street with a van driving along between the two sides, and not one has any sort of reaction to the alien ship. This real shot of the White House (some shots had smaller-scale models) had the CG ship edited in during post production. (Visible on fullscreen DVD.)
Continuity mistake: When the President holds his frightened daughter, in the shot after the alien craft creates a shadow over the White House, there are photographs and a bust of Lincoln on the table beside the President - the view of the photos is not blocked by anything. In the very next close-up of the photos, things differ, such as a large framed photo of the President with the Dalai Lama that appears out of nowhere, between the photo of the First Lady and the photo of the Pope.
Visible crew/equipment: At Area 51's main research facility, Dr. Okun walks up to greet President Whitmore and as his assistant, Dr. Isaacs walks up behind him, the green actor's mark is visible on the floor - he even glances down at it. (Only visible on fullscreen DVD.)
Visible crew/equipment: At the containment lab, just before Dr. Okun unlocks "the vault", three actors' marks are visible. One mark is at the top of the ramp and the other two are visible just past the ramp. (Only visible on fullscreen DVD.)
Revealing mistake: When Jeff Goldblum is throwing a tantrum in the hangar housing the captured alien craft, he knocks over several plastic garbage cans, one of which is clearly labelled "Art Dept" - kind of odd for a top secret underground government military research facility. (01:35:15)
Continuity mistake: When Jasmine grabs Dylan out of the car, his sneakers are white/black with black laces, but when she is kicking the maintenance door, his sneakers are white with white laces, then it switches again in following shots.
Visible crew/equipment: At the Area 51 lab, when President Whitmore is down on the ground in pain, in the shot from inside the lab facing the lab's outer hall, the alien costume only reaches just above the crewmember's waist - the costume straps attached to his pants are visible, as well as his arm. (Only visible on fullscreen DVD.)
Continuity mistake: When David is getting drunk and he's talking to Connie, at one point he slams the bottle down on the counter and a little liquor sprays up out the opening. Then they talk for a second, and he picks the bottle back up to pour himself more, but he now needs to unscrew the cap which was just lying next to the bottle. (01:25:45)
Continuity mistake: When Jasmine sees the approaching fireball she grabs Dylan from the car and begins to run. In the shot from behind, there are double-yellow lines on the road at her feet reaching into the distance, but in the shot facing her the lines have vanished, though she did not change lanes.
Visible crew/equipment: When President Whitmore, General Grey and the rest return to the containment lab to see the live alien, Major Mitchell stands directly in front of the smoke filled lab and the camera equipment/crew are visible in the reflection on the glass. President Whitmore, General Grey and a few others are supposed to be the only ones in front of the three aliens' liquid chambers. (Only visible on fullscreen DVD.)
Continuity mistake: When Captain Hiller is dragging the unconscious alien across the desert, the sky alternates between overcast and perfectly sunny depending on if it's a close up or far off view of Hiller. (01:07:30)
Answer: Remember that the aliens had to interface with our satellite computer code first...David simply "reverse engineered" the code to create the virus. When it was uploaded, they didn't have enough time to combat it.