Wallon Worm Skirts Around Windows Patch Release:
"Wallon's infection process is complicated. Unlike the ordinary e-mail worm that arrives in an attachment to a message, Wallon appears as a link in a message to a Yahoo page. But with redirection, the Yahoo connection leads to another page that delivers an encrypted link to yet another page that delivers a special downloader application.

Microsoft provided a security patch for this vulnerability in April and suggested its application for all currently supported Windows versions. The company describes the update as 'critical' and recommends it for all Windows variants, starting with Windows 98, even for systems where Outlook Express is not the default e-mail reader.… "

http://www.eweek.com/article2/0,1759,1591569,00.asp