unnecessay programmes on internet?

What do you feel if unnecessay box and virus attack you mail and unnecessay form fill box?
One I was cheated like that . I filled the form for the yahoo sign in but next day I can't access on my account . I thought that My password has been changed and used by another. But I am not worried about that because that id has got the old and that should be changed. So I got new email id on yahoo. since then I got my mind to fill the unnecessay form so that email is lost forever.
Have you experienced such mistake and happenings?