Quote
The Bugbear virus infects computers running the Windows operating system and an unpatched version of Internet Explorer 5.5, according to an advisory posted by security company Symantec. A flaw in MIME (the multipurpose Internet mail extensions) lets a malicious program attached to an e-mail message execute when the text of the message appears in Outlook. The software problem was patched by Microsoft almost 18 months ago, but some users apparently have not updated their computers.