Visible crew/equipment: When David introduces the idea of a virus, the first time Major Mitchell shoots at the Coke can the two actors' marks are visible on the floor in front of Julius and Connie, as well as a brown rug at their feet, that are not in other shots. (Only visible on fullscreen DVD.)
Visible crew/equipment: At the club, when Jasmine walks to the mirror in the dressing room her tape mark is visible on the floor. (Only visible on fullscreen DVD).
Visible crew/equipment: When the President stands by "the big tamale" he asks Dr. Okun if he can tell them anything useful about them. When Okun rushes up the ramp as he passes Nimzicki, the actor's mark is visible on the ramp, directly in front of the Secretary of Defense. (Only visible on fullscreen DVD.)
Visible crew/equipment: After General Grey shows the nuclear missile and launch mechanism to Steven and David, when Connie asks, "Why you?", in the next shot just as a woman in a white lab coat passes David, his yellow actor's mark is visible on the floor at his feet. (Only visible on fullscreen DVD.)
Visible crew/equipment: After Russell shows up in the FA/18 with the last missile, when President Whitmore says, "We'll draw them off and it'll be all yours," the set's multiple light tower is reflected on the President's helmet visor.
Visible crew/equipment: When Russell lands his crop-dusting plane and Miguel rides up alongside on his motorbike. The equipment used to help stop the motorbike, at the right position for the close-up, is visible on the ground - but it's gone in the wideshot. (Only visible on fullscreen DVD.)
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.