Direct Access to Model or to use Library?

[eluser]bunal[/eluser]
Thanks

Another quick question.

For security do you prefer splitting model methods.

For example:

Code:

function update_user($username,$data){
  SQL(update user set d = $data where username = $username)
}

Code:

function update_mydetail($data){
  $username = $my_username_in_session
  SQL(update user set d = $data where username = $username)
}

And also do you prefer writing methods for admin and users seperate, or maybe also in different model files?