A family member's PC had a weird virus that I've removed, but it has left behind a trojan horse that won't go away. It only shows up when I scan with AVG:
Nothing else picks it up; Malwarebytes, Avast and Spybot Search & Destory (all run in safe mode) don't find it. I ran HijackThis and the log showed nothing out of the ordinary (using the online analyser).
Googling shows others with the same problem, but I can't find a fix for it.
Any ideas?

Nothing else picks it up; Malwarebytes, Avast and Spybot Search & Destory (all run in safe mode) don't find it. I ran HijackThis and the log showed nothing out of the ordinary (using the online analyser).
Googling shows others with the same problem, but I can't find a fix for it.
Any ideas?