The current version of IE for Macs is effectively three years old, making it an outdated browser compared to its Windows equivalent. In June 2003, Microsoft said it had stopped work on developing the browser.More details over here.
It has now put the final nails into the coffin, announcing that it will not provide any further security updates as from the end of the year. The browser itself will be removed from Microsoft Mactopia download site from 31 January.
Microsoft recommends users to switch to more recent web browsers such as Apple's Safari.