Update Using File::MimeInfo might be the best solution in determining the filetype.

The listing when you sort by "file type" groups together files that map to file types of the same name. Look in "Tools"-> "Folder Options"-> "File Types". If you want to make the two extensions behave differently you can do so in that dialog.

If you want to move all the "wma" files somewhere you could write a File::Find script to do it, or you could use the Windows Explorer search button to look for the files "*.wma"

I don't think that even Windows goes round gratuitously renaming your files (mind you it wouldn't surprise me greatly if it did)

Coming to the point... Is there any way to write a program that will spot wma files that have been named as mp3 files, and rename / delete / isolate them into a special folder? I don't know much about the file format, or even how you would find out what the file format is.

It may be a function of an media player such as Windows Media Player to open a file regardless of extension and divine what it is, then play it appropriately. So I understand your concern. What I would recommend doing here is changing to a different media player, such as WinAmp, where an mp3 is still an mp3. There also are/were similar Windows problems with email, where mime type can or will be ignored in favor of the file extension (or vice versa), allowing seemingly non-executable payloads to be dangerous and/or automatically loaded.

As to the Perl nature of your question, I'd attack this in a low level sort of way, could you try to read the ID3 tag using a Perl module and see if that fails? Still, I don't think you really need to do this. This is just one of many security problems in Windows, and I have not yet seen any exploit using WMA's to launch arbitrary code -- and if you switch media players, you'll be much safer. Not as safer as running Linux, but safer.

Bwaha ha ha. What "integrity" are you referring to?

#!/usr/bin/perl -w
use strict;
use File::Find;
use File::Copy;

# WMA/WMV file signature; See:
#   http://filext.com/detaillist.php?extdetail=WMA
#   http://filext.com/detaillist.php?extdetail=WMV
my $sig = "\x30\x26\xB2\x75\x8E\x66\xCF\x11"
        . "\xA6\xD9\x00\xAA\x00\x62\xCE\x6C";

my @drives = map {$_.':/'} qw( c e );

# Work-around for Win32 bug in File::Find.
chdir $_ foreach @drives;

my @fakes;
find( sub {
  # Skip known NTFS-locked directories.
  $File::Find::prune = 1, return if /^System Volume Information$/;
  return unless m{\.wm[av]$}i and -f $_;
  open IN, $_ or return;
  binmode IN;
  read(IN, my $f16, 16);
  close IN;
  push @fakes, $File::Find::name if $f16 ne $sig;
}, @drives );

foreach (@fakes) {
  print "Fake: $_\n";
  move($_, "$_-fake") or warn "Rename failed: '$_'\n";
}
[download]

Oops, I was not signed on when I posted that!