Although all of us here rekon that Malwarebytes is a good program for getting rid of nasties, my wife was complaining that she was getting fed up of windoze (XP) repeatedly crashing recently. It was only a few months ago that I rebuilt XP on her machine. A scan with Avast revealed nothing, Malwarebytes found nothing, so in desparation I tried good old windoze defender. It found a nasty trojan which it managed to remove. This was clearly well embedded as when windoze boots now it complains that it cannot find a certain .dll but still runs happily. Problem appears to be solved.
P.P.