Margaret,
Its actually impossible for 'iTunes' to give you a trojan. he imported something into iTunes that was affected(if that). iTunes itself had no responsibility for the issue. It is a piece of software from one of the more respected software companies (Whilst I don't like the iPhone the MAC platform and OSX is very very good).
There is LOTs that come free. My whole Opertaing system, and all the programs that runs on it is 'free' .
