I've posted a question that had some legal repercussions in workplace.stackexchange.com, which is off-topic over there, so I'm asking the legal part of it here.
The situation is this. I'm a (inexperienced) system's administrator. I've been approached by my boss about his suspicions that an employee is playing video games at work. I've also been approached by the employee's coworker, who reported seeing weird flashes from his monitor, and that when someone gets close he switches to work related windows. That coworker was motivated to talk to me because he's overburden with work while his co-worker is lagging behind.
One day, after hours, his boss was snooping around on the employee's pc and asked me for help. We found Diablo 3 installed in the pc, and browser history containing some dating websites. Following these findings, the boss asked me to monitor his computer to get concrete data on those activities.
I can do that from a technical perspective, but I worry that doing so without his knowledge might be legally problematic, especially with the dating sites involved, it's possible I may come across very sensitive information.