If your after speed it may matter, since if you have seperate tables for login and member info they will at one stage need to be joined or an extra query will need to run to display the information.
If its security your worried about having data in another table isnt going to stop information being compromised.
IMO, you should really keep data that is relevant to the primary key. If your after Database Optimization look into Normalisation, however keeping the data in one table shouldnt be a worry since it should be relevant to the primary key / key.