    Sentence 1: The virus spreads when  unsuspecting computer users open file  attachments in emails that contain  familiar headings like " Thank You ! ”  and" Re : Details” .    Sentence 2: Sobig.F spreads — uhen  unsuspecting computer users open file  attachments in e-mails that contain  such familiar headings as " Thank You  t," "Re : Details " or " Re : That  Movie."