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Why Old Office documents should be banned

After our suggestion to ignore old style Office documents, it’s clear some folks haven’t changed or still accept the older .doc .xls or .ppt files as email attachments.  That’s a risky thing to do, especially when there’s a common and better alternative.

Mostly it’s because of misunderstandings about the many advantages of the ‘new’ Office document formats .docx .xlsx or .pptx.

Let’s go over the main advantages of the ‘new’ Office documents formats and why you should NOT open any document that arrives in the old format

To call the Office document formats ‘new’ is a bit silly now.  It’s been over 15 years since .docx .xlsx .pptx and others became public.  The new formats are well established and the default in most cases.

Why do people still use the old document formats?

The only ‘legitimate’ use of the old formats is to spread viruses, ransomware or steal data.  Most viruses using Office documents rely on the older document formats (usually Word .doc) to spread.

Some organizations have stuck with the old formats out of habit and unwillingness to change.  The danger in those formats hasn’t been properly explained by Microsoft or the anti-virus industry generally.

We’ve seen too many people and organizations with Office 2007 or later still opening and making .doc in Word, .xlsx in Excel or .ppt in PowerPoint even though the software can do better.

Hackers just love these people, companies and governments because they are easy pickings.

What smart Office users do

Smart and cautious Microsoft Office users have nothing to do with the old document formats.

Any incoming .doc .xls or .ppt files are not opened at all because of the infection risk.  Some IT admins will block any email attachments with those extensions even if they pass anti-virus scans.  If such a document arrives from a legitimate source, reply asking for it to be resent in a safer format – see Free and secure conversion of .doc .xls or .ppt to the new Office formats.

Only the new formats .docx .xlsx .pptx etc are sent out or shared.

If you have .doc .xls .ppt files sitting in old or archive folders, that’s OK.  It’s probably not worth the time/trouble to convert them.  When and if the files are opened, convert to a new format (Save As …).

Microsoft isn’t helping

Microsoft doesn’t usually make a distinction between the formats when describing a security hole in Office.  They talk about the cause being a ‘malicious Word document’ without saying if it’s in the new or old format.

Tell the two apart

To the human eye, it’s easy to tell old and new formats apart.  All the older formats have 3 letter extensions (.doc) while the new formats have 4 letter extensions (.docx).

Access 2007 and later use 5 letter extensions (.accdb etc).

Why the new document formats?

Why did Microsoft create these new document formats?  They have many benefits over the old formats.  The open source industry was developing these improved formats and Microsoft joined in the task.

More reliable

The new formats are very different to the old ones.  New documents are coded in a very different way with XML formatting for the most part.  That makes no difference to daily users but there are advantages you’re not aware of.

.docx etc are easier to recover if they are corrupted.  The XML structure means that a ‘bad’ section doesn’t mess up the entire document.  The good sections can be restored more easily.

More secure

Password protection in the new document formats is a lot stronger than before.

Less likely to be hacked

The default document formats cannot run macros at all.  .docx  .xlsx  .pptx are macro free.  Even if a hacker tries to hide a macro in a .docx file, Word won’t run it.

Office has other protections against unwanted macro intrusion but the main one is simply not allowing them to run at all in .docx etc files.  The last decades experience shows that this simple measure is one of the best protections against Office document infection.

If you need a macro in an Office document, they have to be saved with an ‘m’ ending  .docm  .xlsm .pptm .


The files are smaller because the contents are compressed.  Sharing files via email, messaging etc is faster.

Modern Office documents use the well-known ZIP system.  Again, this isn’t something you need to know or worry about – Office figures it out for you.  See Myth Busting about Office document formats

There are other advantages to the ‘new’ formats but they are the main ones for the public.

OpenDocument formats (.odt etc) are very similar to the Microsoft formats (XML based, ZIP compression etc)..  Microsoft worked with the open source teams on these new formats before branching out on their own.

Google Docs supports .docx and .xlsx

Beating Bots, Spies & Cock-ups – Safely – securely send files and documents

Sensitivity settings add security for Office documents

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