I keep getting ai123456789.ai duplicate files, how can I stop this?

I got a refurbished Imac here at work, but 1/3 of the time when I save a file it also saves a duplicate file named something like ai123456789.ai. I'm connected to a server, but my other IMac that I also still am somewhat using because Illustrator on the new one is slow to save doesn't have this problem. I can't delete them, so I moved them into a delete later folder. How can I stop this?