Avoiding multiple logins to an account from different locations
<p>I want to avoid multiple log ins of the same user from different locations, or I want to give a warning or something to the user's mail to indicate there is another log in to their area.</p>

<p>How can I identify a user's multiple log in from different location at same/recent time? I think some flags and IP checking in a  table may be a solution, but are there others?</p>

<p>update:
i think the session or cookie may help(for a single machine), like for first login creating a active key and store it into that machine at first login, and every time the user login in that machine check these cookie value too.. so if either he uses proxy it can helpful for identifying the user.. isn't? i/m not sure it will produce any security problems or something?</p>
