sub mask_it
{
    my ($instr) = @_;
    my $retstr = '';
    while ($instr =~ /[0-9a-z]/i) {
        if (/^([^0-9a-z]*)([a-z]+)/i) {
            $retstr .= $1;  #pass non-alphas as-is
            my $orig = $2;  #replace alphas with new ones
            $retstr .= join('',map { chr(65+int(rand(26))) } split(//,$orig));
        }
        elsif (/^([^0-9a-z]*)(\d+)/i {
            $retstr .= $1;  #pass non-digits as-is
            my $orig = $2;  #replace digits with new ones
            $retstr .= join('',map { chr(48+int(rand(10))) } split(//,$orig));
        }
        $instr =~ s/^(\W*)$orig//; #remove from input
    }
    $retstr .= $instr;  #pass on anything that's left over
    return $retstr;
}