Identity Thieves Spying on Your WiFi?

The other day I sat down at my home computer, an iMac, and clicked on the Microsoft Word document where I keep all my important data: passwords, code numbers, URLs for work-related websites, and, of course, credit card numbers. But something weird happened when I tried to open it. I saw a message that read: “File is in use by another user.” What could “another user” mean, I wondered? Could someone have hacked his way onto my machine? Slowly, I pieced together what could be going on. Someone might have remotely accessed my computer and read my personal records.