window service: How to get timestamp when user logged in into the system

Question

Hi all,

I want to write a window service that send the email as soon as the user will logged in into the system(Computer).

I want to know the user and the time i.e. at what time he/she logs in.

With the help of system.security,principal i get the current user but how to get the loggin time.

Pease help!