Microsoft Internet Explorer 6 and 7 embeds FTP credentials in HTML files that are retrieved during an FTP session, which allows context-dependent attackers to obtain sensitive information by reading the HTML source, as demonstrated by a (1) .htm, (2) .html, or (3) .mht file.
http://secunia.com/advisories/26427
http://blog.washingtonpost.com/securityfix/2007/08/ftp_files_expose_web_site_cred.html