Think the odds on the cause might just be nicely weighted towards the son who meddles. All of a sudden, I might also suggest checking the spyware status and if necc. installing Windows Defender, Adaware or Spybot for them too. (all free)
Why is it, that when anyone mentions sons, daughters and their friends, I keep thinking of those 'orrible mobile phone ringtone sites?
Conan the crusty