IE8 changes downloaded Office files to .zip. Why and how to deal with it???

I understand what zip files are, and I understand Office 2010 files are zipped files without the zip extention, but why does IE8 change downloading a .ppam file to a .zip file??? FireFox downloads it correctly as a .ppam. Are users expected to know to change the extension back to ppam? Is this the default? Is there a way to turn this off? Will IE 9 have this same undesirable behavior?

Edit01: I read that IE outsmarts itself in guessing the file type and then makes it's own decision to change the extension to something maybe incorrect. The server administrator has to add extra MIME information on the server to correct IE's faulty logic. Is that about right?

Thanks,
Melina

 

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Last updated October 23, 2018 Views 12,263 Applies to:
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The problem is on the server and involves compression as well as ISA (Internet Security Acceleration). See this related discussion: http://www.smallbizserver.net/Forums/tabid/53/view/topic/postid/110538/Default.aspx
~Robear Dyer (PA Bear) ~ MS MVP (IE, Mail, Security, Windows & Update Services) since 2002 ~ Disclaimer: MS MVPs neither represent nor work for Microsoft
--
~Robear Dyer (PA Bear)
Microsoft MVP (Windows Client) since October 2002

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Hey Melina,

 

Again I can’t speak for the other browsers, but MIME sniffing/information is used to protect users from malicious code being executed. Here is an excerpt which explains how this could happen:

 

Why is this change important?

If file type information is misreported by the server and that information is saved to the computer, a dangerous file could be incorrectly executed later. For example, Internet Explorer might download a file that appears to be a text file. If the file can’t be loaded by its MIME handler and has a .doc file name extension, the .doc file might run in an application such as Microsoft Word without prompting the user. In Microsoft Word, the file may be able to use active content, such as a macro, to run a program (such as a virus) on the user’s machine.”

Reference:Internet Explorer MIME Handling Enforcement

 

MIME sniffing would sniff the file and recognize it as a macro and not a .doc file, thus giving the user more information about a potentially malicious file.

 

This can cause cases such as this where a file is sniffed and determined to be a .zip instead of an Office file, but this can be corrected by getting the correct information on the server providing the files.


Steven
Microsoft Answers Support Engineer
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