That was just the office sprite. You know, the thing that takes the last of the coffee and doesn't make a new pot, eats other people food in the breakroom fridge, takes your favorite pen out of your desk, gets your boss to come around in during the few minutes you stop to take a break, etc.... .
You're one of the few lucky people to see it.
That really is cool. Golf ball size. I've seen orbs myself. The ones I've seen were just pinpoints of light.
Tonight, leave some of your work at the terminal where you heard the typing. Hopefully, by morning it will be done.
Any suspicions on who these ghosties might be?