Track composed by Michiel van den Bos
Ah, UNATCO. One of my favourite tracks from the entire Deus Ex soundtrack and it's not just me that loves it; there are plenty of remixes of this track if you're willing to do a quick search.
So what else can I say about UNATCO? Well, UNATCO is an acronym that stands for the United Nations Anti-Terrorist Coalition and it's the organisation that JC Denton joins at the beginning of the game. Back when the game was initially released, there was even a fake UNATCO website if you visited http://www.unatco.org, however this was taken down shortly after the September 11th attacks (the domain has since been reclaimed by a fan though).
There are so many memorable quotes while you explore UNATCO headquarters including Gunther Hermann's complaints about the maintenance man as well as Joseph Manderley scolding you and telling you to "behave like a professional, that's an order!"
Another cool thing about this track is that it's not actually composed by Alexander Brandon... I know right? When I was younger, I used to think that the entire soundtrack was composed by Alexander Brandon, foolishly not realising there were other collaborators too including the talented Michiel van den Bos.
Anyway, enjoy listening to the music in this video which contains the main theme from 0:00, the conversation theme from 1:32 and the combat theme from 3:15.