Shows way too much online use

I have the time settings so that it monitors "actively using" only but at 9am this morning it showed that one of my children, who is only authorized on one computer, had been online for 18 1/4 hours today. In a recent weekly report it showed the same child had been online for 72 hours in one day.

 

His laptop is running XP SP3 and I always keep NOF updated.

 

Any ideas?