Factual error: When the porter first gets ready to shoot at the terrorists (after Ryback falls off the train) he goes through a series of verbal instructions to remind himself what to do. The very first thing he says is "safety off". The problem is that the gun he is using is a Glock pistol. Glocks use a device called a "safe-action trigger" but they don't have a manual safety that you turn on and off.
Factual error: The film's plot violates the third of the Ten Immutable Laws of Security by Scott Culp. The premise of the law is: When one has physical access to a computer system, given enough time, he can take over the system. In the film, the reverse happens: Dane takes over an ATAC site remotely while people inside (who have complete physical access) cannot do anything to wrest the control back. In the real world, it is usually possible to simply cut the connection cable or antenna and take control back. (Even Windows XP and later have such simple lockdown provisions as part of Windows Firewall.) After the lockdown, the passcodes can be changed and other measures taken.
Factual error: The main premise of the film is ATAC's loss of control over their orbital weapon and their attempt to prevent it from doing damage. According to ATAC, they needed to know where the weaponized satellite is, so that they can lock onto it and send it a self-destruct order via radio waves. This isn't how the real world works: Radio waves emit in all directions from its transmitting source. The location of the satellite need not to be known; only it must be within the reach of the ATAC's signal.
Factual error: The terrorists supposedly stole the helicopters from a fictitious National Guard Base near Leadville Co. (No such base exists), but when they take off in the helicopters you can see the eastern slope of Pikes Peak in the background. Indicating that the helicopters are taking off from an airport just east of Colorado Springs.