well, all these posts have some points your friend's computer had been trojaned or third party.

i suggest check all the autostart programs with computer, delete some wired programs.
if a password had been changed that meant some one found out his password, or crack his password. so somebody is making fun with your guys.

if nothing workout, i think you just uninstall all the programs which caused programs, and reinstall them, or reinstall your window if you have a window's cd.