In Back to the Future Part II, when Jennifer was in her future house in 2015 she witnessed the old Marty getting fired after being provoked by Needles into sticking his card in the slot. What kind of financial operation was that and what was illegal about that?
Update: One more thing: if Fujitsu knew that Needles was involved then why wasn't Needles fired as well?
Unless it's explained in the novelization, it doesn't look like we're meant to know exactly what the operation was; it's suggested that it's some kind of easily missed financial malfeasance (like Salami Slicing), but the nature isn't defined. (Details, had they been provided, would likely have gotten viewers focusing on the moral details / practical chances of getting away with it, etc.)
Watching the scene, here's the relevant part transcribed:
Needles: Did you take a look at that little business proposal of mine?
Marty: I don't know Needles.
Needles: What are you afraid of? If this thing works, it will solve all of your financial problems.
Marty: And if it doesn't work, Needles, I could get fired. It's illegal. I mean what if the Jits is monitoring, huh?
Needles: The Jits will never find out.
I think it's meant to be unspecific, and we know all we're meant to --
In both the draft script (where it's not mentioned at all), the final revised draft script and the novelisation it's simply described as a "plan", one that has something to do with Marty's access card.
‘Hey, Needles,' Marty replied, trying not to sound nervous.
Needles didn't seem to notice. Instead, he launched quickly into exactly what Marty had to do if their little plan was going to work. Somehow, whenever Needles explained this sort of thing - in all the years they had known each other, ever since high school -it always sounded so easy.
So what do you say, Marty?' he finished breezily, once more flashing the grin that had gotten Needles to a position in the organization that Marty could never hope to reach.
According to the usually highly accurate KristenSheley.com website, there was a brief mention in a revised draft script that it was a "902 deal" but beyond that, no further description. Note that the order of events play out slightly differently.
Inside the McFly's 2015 house, things play out similar as they do in the film, though there is more conversation between Lorraine and George. We learn, for example, that Marty blamed everyone but himself for the race with the Rolls Royce. When Marty arrives home from work, he takes a message from a "Harrison" at work, who tries to cajol him into the "902 deal" at work. Marty is reluctant, as he is up for a promotion, but the chicken thing provokes him. Fujitsu pages him during dinner to fire him, as Harrison turned Marty in after "catching" his illegal transfer. Even when Marty explaines he was tricked, his boss still says he's fired "for being stupid enough to fall for it."
