Changing the registered email at those places can be helpful too. If the stalker can access his Yahoo! account and that's the registered email at Facebook, etc. then changes to those accounts would be useless.
He should also check his firewall/sharing settings. If he's properly protected, someone should not be able to get into his computer from the outside.
The ones I pity are the ones who never stick out their neck for something they believe, never know the taste of moral struggle, and never have the thrill of victory. - Jonathan Kozol