Neutralizing MM256.DAT and MM2048.DAT files
by ZenGuy+

The Problem

The main problems with the MM256.DAT and MM2048.DAT files have been outlined in detail elsewhere (reverser's What's behind the mm256.dat and mm2048.dat files?) .  Suffice it to say that any files such as these that:

can be considered to pose a potential security or privacy threat.  Ominously, these files cannot be deleted by users, and multiple copies are stored in various locations on the user's hard drive.

An Interim Solution

The simple procedures outlined below are intended as a first step in creating a workaround to this problem, at least until someone finds a better solution.  It is also hoped that the suggestions below might lead to feedback and suggestions for improvement from others.  Why not offer your suggestions to Reverser?

Here are the basic steps to neutralize these files:

Step 1:  Locate the files on your hard drive

Copies of the MM256.DAT and MM2048.DAT files can be found in any or all of the following locations. Check the table below and make a list of where the files are located on your hard drive. Check the following locations:

C:\WINDOWS\Temporary Internet Files\CACHE1 (Note: Actual directory name may be different for IE-4 users)
C:\WINDOWS\Temporary Internet Files\CACHE2 (Note: Actual directory name CACHE1 different for IE-4 users)
C:\WINDOWS\Temporary Internet Files\CACHE3 (Note: Actual directory name CACHE1 different for IE-4 users)
C:\WINDOWS\Temporary Internet Files\CACHE4 (Note: Actual directory name CACHE1 different for IE-4 users)

Step 2:  Edit each MM256.DAT and MM2048.DAT file with Windows Notepad, deleting all content found in each file. 

This is fairly self-explanatory, but there is one trick needed to save the file properly.  Just open each file in Notepad, select all the existing content, then press the Delete button.  Now save the changes you've made to the file, using double-quotes around the filename.  This will ensure the file is saved with the proper extension (i.e. '.dat').


By the way, once the file is saved, its file size should now be 'zero'.

Step 3:  'Lock' each file by changing its 'attributes' to 'Read-only'.

This is easier than it sounds.  Simply go to Windows Explorer, navigate to the proper directory, right-click on the file, click on 'Properties', then check the 'Read-only' checkbox and click 'OK'. (For extra protection, click on the 'Hidden' checkbox too).


Step 4:   Congratulations -- the MM256.DAT and MM2048.DAT files have been neutralized. You are done!

Other Tricks:

For those who want to go further than simply locking the MM256.DAT and MM2048.DAT files, here are some other suggestions.  

Deleting Existing Cookies

Please note: For this suggestion it is recommended that you also add the 'hidden' attribute to C:\WINDOWS\Cookies\MM2048.DAT
as in 'Step 3' above.

To automatically delete Internet Explorer 'cookies' when booting up, simply edit your C:\AUTOEXEC.BAT with Notepad, adding the following 2 lines to the end of the file:

echo Clearing C:\WINDOWS\COOKIES ...
echo y| del C:\WINDOWS\COOKIES\*.*

then save the file. This will delete all stored cookie files, but leave the 2 locked '.dat' files intact.

Deleting Internet Explorer's Cache Files

IE's cached files can also be deleted upon booting up your PC, for extra privacy, and to conserve hard drive space. Edit your C:\AUTOEXEC.BAT with Notepad, adding the following 6 lines to the end of the file:

echo Clearing all C:\WINDOWS\TEMPOR~1\CACHE files ...
echo y| del C:\WINDOWS\TEMPOR~1\CACHE1\*.*
echo y| del C:\WINDOWS\TEMPOR~1\CACHE2\*.*
echo y| del C:\WINDOWS\TEMPOR~1\CACHE3\*.*
echo y| del C:\WINDOWS\TEMPOR~1\CACHE4\*.*
echo y| del C:\WINDOWS\HISTORY\*.*

NOTE: It is recommended that you double-check the directory name of the CACHE1, CACHE2, CACHE3, and CACHE4 directories. If you have ever used IE version 4, these directories will likely have a slightly different name.  If so, just edit the lines shown above accordingly, and put these instead in your C:\AUTOEXEC.BAT.

Now save the file.

Some Warnings

As noted previously, the procedures outlined above are experimental.  Please note, therefore, the following known issues and limitations.

Internet Explorer Error Message

Once the '.DAT' files have been 'locked', starting up Internet Explorer (I have only tested version 3) will produce the following seemingly serious error message:

Oh my!  Sit back and be very amused as IE screams bloody murder because it can't get its paws on those nasty files <heh heh heh>  (Kind of reminds me of HAL in the movie '2001: A Space Odyssey' as he's being shutdown :-).  )

In fact, the 'serious error message' turns out to be mostly a non-issue:  IE appears to function quite normally after the user simply presses 'OK'.  Note that it is certainly possible that no cookies can now be saved, but this user considers that a good thing; besides, you should probably be using Netscape or Opera anyway if you value your privacy at all, right? Still, this does need to be tested. And speaking of testing...

Scope of Testing

The above procedures have so far been tested with the Windoze 95 operating system.  Your mileage may vary (YMMV) with Windoze 3.1 or Windoze NT.  Also I have not tested the procedures with Internet Explorer 4, only IE 3. The Netscape browser works just fine, and I assume that Opera would be alright too. Hey, why not do some quick testing on your operating system and send the results?  Make your own contribution to the battle for online privacy!

Thanks for your time -- I hope this essay proves helpful to some readers. :-)

Last modified: December 20, 1998