To disable yahoo sync in apple address book and apple ical.
go to the dock
click on finder
go to the menu bar
click on the go menu
from the go menu chose applications
double click on address book
when address book opens, go to the address book menu, and chose preferences.
the general preferences window will pop up
click on accounts tab
from the accounts list click on “on my mac”
uncheck “synchronize with Yahoo!”
close the window
quite address book
if you still have the issue. OR “synchronize with Yahoo!” was not checked in address book
open ical in the applications folder
from the ical menu, chose preferences
click on the accounts tab
the accounts list may list a yahoo account. if so, click on it, you can click on it and then click on the “-” to remove the account.