Ref: http://www.winvistatips.com/security-log-eventid-529-smtp-t673781.html
Ref: http://www.pcreview.co.uk/forums/thread-1596278.php
Bad guys are trying to authenticate server via port 25.
How to reproduce this log:
# Type telnet 25,and then press ENTER.
# Type EHLO , and then press ENTER.
# Type AUTH LOGIN. The server responds with an encrypted prompt for your user name.
# Enter your user name encrypted in base 64. You [...]