You should check that no username match the username_db

open PAGE, "$data_reg" or die "Can't open $data_reg: $!";

while (my $line = <PAGE>) {
    ($username_db,$password_db,$email_address_db,$name_db,$spare) = sp
+lit "\t",$line;
    if ($username eq $username_db) {
      $check++;
      $found_user++;
      last; # exit while
    }
}
unless ( $found_user ) {
  $problem = "Unfortunately we cannot find reference to the username s
+upplied.<br> Please check with the webmaster of this site.";
  print "$problem";
  exit;
}
close PAGE;
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