After he is taken to a frightening dystopian future resulting directly from his work, a disillusioned software developer returns to the present, intent on putting an end to his firm's nefarious plans.

How about this:

"After getting a glimpse of a dark future, a software developer must destroy his own work or the future will become reality."

Yes, it's the company he works for that presents the greatest opposing force to him trying to take them down. Should that be clarified in the logline?

Also - the software he's working on leads to the invention of time travel, which he discovers the head-honchos at his company will eventually use to overthrow the government and install a totalitarian regime. Without padding out the logline with too much excess information, do you think I need to be more specific about that?

point taken about "frightening dystopia." I'm testing out the language, because it needs to sounds as disastrous as possible.

Yes, it's necessary for the logline to contain the trip to the future. Not only is it the inciting incident (without it, the logline would be about a character trying to destroy the company he works for ... which seems a little crazy but far less compelling), but it also presents the stakes of the story (should he fail to destroy his company in the present, then a horrible future awaits all mankind).

In what way do you mean to describe why he is frightened? You mean, get specific about the elements of the future that cause him to not want that future to eventuate?

Finally, again testing language, 'disillusioned' was the word I chose because I want to convey the character's inner journey - he goes from questioning his faith in God to a becoming certain of the existence of fate (and therefore a master plan) through the course of the film. The one word i could think to distill the loss-of-faith state that the character sets out upon his journey with is disillusioned. If you have something more precise, I'm very open to it.