"The "extremely critical" Excel vulnerabilities are found in Microsoft Office 2000, Office 2003 and Office XP, as well as in Office 2004 for computers running Apple's Mac OS, according to a separate advisory from security company Secunia.

Attackers are sending e-mails with malicious Excel attachments and are hosting Web sites that house Office files that attempt to take advantage of the security flaws, according to Microsoft. Once an attacker exploits the vulnerabilities, they can gain control of a person's system remotely."

This effects EVERYONE with Excel, even Macs...  Be sure to check the security advisory from Microsoft and get all needed updates!