We can't - we have no idea how your are handling your log in.
Are you using the standard Membership provider? If so, then the answer is on the MSDN page:
http://msdn.microsoft.com/en-us/library/yh26yfzy.aspx[
^]
Or are you "home brewing" it? In which case, we have no idea what you are doing, so how could we possibly comment?