Can an employer disclose private information viewed on a company computer?
I had some private chats with a co-worker on a company computer (stupid of us). We discussed other coworkers and when my boss chose to review the screenshots and saw the chats, he decided to tell the other employees what we had said about them. Furthermore, he threatened to tell my co-worker's wife about something he had said (didn't specify what), saying "Oh, she'll care!" My friend says this is harassment. Clearly we shouldn't have shared personal stuff on the computer. Does that mean my boss has carte blanche to reshare that private information? What if it had been a private medical result?
Unfortunately, as you surmised, if exchanged messages on a company computer, it is not private. While it was inappropriate for your employer to share the information with other people, it's not clear that he had any legal duty or obligation to not do so. The information was not obtained in a context which would extend or even imply a legal duty to keep it confidential, such as, for example, when someone fills in their current or last salary or social security number when applying for a job; the context obligates the recipient to use the information only for the stated purpose, the job application. Here though, the situation is closer to that of the two of you being overheard while chatting by the water cooler; someone overhearing a public conversation generally can repeat or transmit it to others.