This doesn't match your sample output,but it does match my understanding of your description.

use strict;
use warnings;

my %oHash;
my %count;
my $best = 0;
my $bestCode;

while (<DATA>) {
    chomp;
    
    my ($code) = /\s+(.*)/;
    next if ++$count{$code} <= $best;
    $best = $count{$code};
    $bestCode = $code;
}

print "Found $best occurances of $bestCode\n";

__DATA__
Affy:HG_U133A:213119_at:74:303; ENSG00000123643
Affy:HG_U133A:213119_at:542:439;        ENSG00000123643
Affy:HG_U133A:213119_at:658:369;        ENSG00000123643
Affy:HG_U133A:213119_at:199:255;        ENSG00000123643
Affy:HG_U133A:213119_at:436:453;        ENSG00000123643
Affy:HG_U133A:213119_at:324:381;        ENSG00000458158
Affy:HG_U133A:213119_at:584:557;        ENSG00000123643
Affy:HG_U133A:213119_at:234:507;        ENSG00000123643
Affy:HG_U133A:213119_at:482:429;        ENSG00000123643
Affy:HG_U133A:213119_at:608:451;        ENSG00000458158
Affy:HG_U133A:213119_at:356:297;        ENSG00000123643

[download]

Prints:

Found 9 occurances of ENSG00000123643

[download]
DWIM is Perl's answer to Gödel

In reply to Re: Counting hash values by GrandFather
in thread Counting hash values by MonkPaul

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