Computers running Outlook Express 5.5 are not vulnerable to this issue. Outlook Express 5.5 includes this update.
This update resolves the "Persistent Mail Browser Link," "Cache Bypass," and "Malformed E-mail Header" security vulnerabilities in Outlook Express. Download now to prevent a malicious user from reading e-mails and files on your computer, or using your computer to send damaging e-mails to others. These vulnerabilities do not give a malicious user the ability to add, change, or delete files on your computer.