My computer is used by my kids, who are 10 and 15 years old. I want to monitor that what they do in my absence. I want to see when they turned the computer on or off; which websites they opened; whom they chatted with; screenshots every x minutes; etc.
I do not necessarily want this info e-mailed to me, or for their passwords to be saved. I just want to monitor their activities.
How can I keep track of my kids' computer use? Does there exist software for this?

