Failed login attempts on Mac

REF: http://apple.stackexchange.com/questions/120668/ddg#120670

You can use this Terminal command:

cat /private/var/log/system.log | grep "Failed to authenticate"

Feb 11 16:48:04 g authorizationhost[15313]: Failed to authenticate user  (error: 9).
Feb 11 16:48:06 g authorizationhost[15313]: Failed to authenticate user  (error: 9).