acFTP is an open-source FTP daemon for Windows platforms (http://www.sourceforge.net/projects/acftp) that offers more functionality than many proprietary servers (including the MS FTP service). The authentication code of acFTP contains a flaw -- specifically, the server treats users as logged in without a valid password. This results in mis-representation of server activity in log files, and possibly privilege elevation. For example: USER private PASS # This leads it to reject my password, but I can not log in with another set of credentials, and my log activity appears as "private" instead of the appropriate "-" or "***".