Prevent multiple login using the same user name and password

Question

I am developing an application that needs to prevent multiple login using the same user name and password.

If it happens on the same machine then obviously we need t

Answer 1

Take one extra field in table with the column name say "IsLoggedIn" as bit field and set it to true until the user is logged in. As soon as user logs out set it to false. This need to be done for session expiry time also. As soon as the session expires this field should be set to false automatically using triggers or thru SP call

good solution is still welcome