theuser is correct regarding Klez. Klez usually comes with with trojan "Elkern" or similar.. simply depends on what patches you DIDN't have installed and if you were using Outlook express AND were running with the preview pain enabled.. simply previewing the infected message infected you.. cool huh.. but if you had all the ie 5.5 or IE 6 updates you "shouldn't have a problem (one of the reports on klez and bugbear claimed that IE6 was imune..what a joke.. most of the systems we fixed had IE 6 and 6.1)

Cheers