Old and unused Apple ID removal from iTunes?

[totemynote]

I bought a used computer that already had a iTunes account on it. They let me keep their music but I registered my own account and for over two years have never had problems using iTunes. I just updated iOS 5 on my brand new iPhone 4S. At the first to sign in prompt on the device the Apple ID text field had the previous owners ID already there like it was a cookied. I deleted their ID and signed on with mine and have no problems so it may not really matter but it is disconcerting to me.

How can I remove the previous owners info completely?