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MP43DECD.dll and MPG4DECD.dll


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I ran a malwarebytes scan after being suspicious malware got onto my computer. The scan found that the files MP43DECD.dll and MPG4DECD.dll were malware, but when I do a search for these files, it says they're from Microsoft and are associated with other files in the C:\Windows\system32 folder.


I not 100% sure what to do. I also saw that someone else had the same results. I don't want to delete legit files but when I look at the files to see when they were accessed, they were accessed earlier today, about the same time I was on the Internet (but not sure if it was the exact time when I became suspicious of malware).

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My daily Threat Scan also detected a problem with MP4GDECD.DLL and MP43DECD.DLL.


I have image backups of my Drive C: from as far back as June, taken about every 3 weeks. All image backups contain these 2 files, dated 18/10/2006. All versions of these .dlls in these image backups are now detected as a virus by Malwarebytes - Trojan.Tagak. They were not detected as a virus back in June, for example.


So I believe that today's update of Malwarebytes is probably incorrectly detecting these as a virus. But I'm not sure - the only way to be sure is for MWB to confirm the status of your uploaded files.




MP4GDECD.DLL and MP43DECD.DLL are MP4 decoders used for watching videos, eg. by MWP. 

I recently upgraded a free program called DVD Styler. I scanned it before install, but it is possible that DVD Styler v2.9.4 came with this trojan.





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I believe this was fixed already. Unfortunately without the files and the detection scan reports it's real hard for us to tell, because we always need files to evaluate.

Please update your Malwarebytes database and let me know if this is still detected. If so, then please attach the files so we can fix it.



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Thanks Mieke - that was a quick response!

I just updated to 2015.11.27.02, and then scanned the 2 dll files contained with my image backups. This time, MWB says they are OK.


So can I presume it was a false positive and restore these files? I've never done a restore before. Presumably, I just go into MWB History, click on the 4 entries (2 x dll files, 2 x Registry entries) and select RESTORE?

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I am reading all of these comments and becoming quite disheartened as the exact same problem happened to me.  I wish now I came here (my judgment mistake!) rather than contacting Malwarebytes by email to their support.  I wrote to inquire if I shoud delete the MP43DECD.dll and MPG4DECD.dll and the other two that showed that they were Registry files, and someone at Malwarebytes named Larry replied that it was okay to delete them. 

Now, I am learning that I should not have done that.  So far I have been able to view Youtube and I have a DVD in playing, but it looks like I am not able to get the files back via a system Restore.  I have a Windows XP computer.  Larry wrote that I can expect more issues because my computer is XP.  Now, come to find out here that these all were False Positives! 

So, I guess if I can't restore them or reinstall them somehow (doubt if Microsoft will help me out on this issue since I have Windows XP), like someone else here wrote we are just out of luck.  So, I have learned a valuable lesson about the value of just leaving some things in Quarantine until you have checked everything out including come here!  Thank you. 

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Linda – I'm running XP and I, too, encountered the MP43DECD.dll and MPG4DECD.dll (and registry) false positives. I only quarantined (didn't delete) them.

Have you tried to recover your deleted files via XP's System Restore? I don't know if it would work for you but it shouldn't hurt to try. You might need to temporarily disable antivirus first or you could end up having to reinstall it.

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If you are having troubles restoring the files for whatever reason, good chance you can uninstall then re-install Windows Media Player.

Uninstall/re-install instructions here:


Failing that.....

You can download the stand-alone installer here:


The download page will ask you to validate Windows before you can get the download.

Once you have the download, you should be able to re-install it.


You all likely want to look into upgrading your OS... XP is no longer supported by Microsoft & many other apps will soon follow.

Because more & more programs are no longer going to support XP, this leaves you especially vulnerable to security issues.

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