source: http://www.securityfocus.com/bid/2490/info

Eudora uses Internet Explorer to assist in the viewing of html messages if the 'Use Microsoft Viewer' option is enabled. Eudora also has a 'allow executables in HTML content' option, which the documentation recommends be disabled for securithy reasons. It is possible for an attacker to excecute arbitrary code on a remote system even if 'allow executables in HTML content' is disabled, if the 'Use Microsoft viewer' option is enabled. 

http://www.malware.com/you!DORA.txt