Last night, Cisco (who now owns WebEx) posted a bulletin about a buffer overflow in the WebEx Meeting Manager ActiveX control.  This one looks like it has the potential to be serious, so if you use WebEx, you are advised to read the Cisco advisory and update or set the killbit.

References:

http://www.cisco.com/warp/public/707/cisco-sa-20080814-webex.shtml

http://nvd.nist.gov/nvd.cfm?cvename=CVE-2008-2737 (not live yet)