do
{
    my $p = $packets[0];
    foreach my $l ($level..length($p))
    {
        foreach my $pos (0..length($p)-$l)
        {
            my $str = substr($p,$pos,$l);

            next if exists $all{$str}; # if we've already found this
                                       # string somewhere else, exit
                                       # this iteration 
            my $num = 0;
            for (0..$#packets)
            {
                if ($l <= length($packets[$_]))
                {
                    pos($packets[$_]) = 0;
                    while ($packets[$_] =~ /$str/g)
                    {
                        $num ++; 
                    }
                }
            }
            unless (exists $all{$str}) 
            {
                $all{$str} = $num unless $num < $threshold;
            }
        }
    }
    shift(@packets);
} while ($#packets >= 0);