In some juridictions (mostly EU countries I think ?) your employer would be at fault if they gathered personal information (for instance a sexual orientation you didn't disclose) from a personal account you used on a work computer. Or from anything you explicitely marked as personnal, even if it's on your computer. They might still delete the data indiscriminately, just shouldn't access it.

Being at work, on company's hardware, isn't enough to completely void your expectation of privacy.