Microsoft has released an update to Internet Explorer 4.5 and Outlook Express 5 for the Mac.

Internet Explorer 4.51 and Outlook Express 5.01 is a patch that addresses some important security issues affecting versions downloaded before December 21, 1999.

The patch fixes Internet Explorer bugs relating to certain certificates (which provide user security) that will expire at midnight on December 31, 1999. Accessing them after that will prompt an "expired certificate" warning.

The update fixes a JavaScript problem – users may have trouble entering sites that require JavaScript, such as Citibank. This problem only affects users who recently downloaded Outlook Express 5, and use Internet Explorer.

Finally, a security issue in Outlook Express has been fixed – the issue makes it possible for a malicious sender to send an MHTML message to an Outlook Express 5 user, which would then download a file to the default Download folder without the user knowing. The download would have to be opened for any damage to occur.