Sometimes your computer can be hijacked by all kinds of stuff. That has happened to me a few times – I have some part-time work looking at websites and sometimes you do pick up stuff.
As far as the registration screen goes, I think you just need to include the basic details and the easy anti-spam question. The section asking about hobbies, occupation and other details such as your yahoo address can be left empty. So just the top section needs to be filled in.