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To protect against viruses, you should read the extensions on all email attachments - if you can.

Interpreting file extensions

It may be possible to tell if an attachment contains a virus by looking at its file extension. The classic virus extensions are .exe and .vbs.

But there are two problems here. The first is that in a regular viewing window, Microsoft Outlook cuts off the names after 17 characters (or less). Not surprisingly, virus makers go for longer filenames, so you can't read the extension.

If you want to see the full name in Microsoft Outlook you need to right click on the mail (without opening it) and place your mouse over View Attachments in the menu that appears. This works most of the time but not always (hello Microsoft, anybody listening?).

Dangerous extensions

The second problem is that techniques exist for giving dangerous files almost any extension you care to name (See the last paragraph of Displaying File Extensions). Which means that looking at extensions isn't all that helpful.

My current advice is not to open any attachments unless you expected to receive them. In other words, only open an attachment if you previously arranged for it to be sent to you from a source you believe to be safe. Never open any attachment that arrives out of the blue. And don't open attachments from friendly sources if their arrival is an unscheduled surprise, especially if they come with nothing more than a brief and generic covering mail.

I used to list all dangerous extensions here, but there are now so many there isn't much point. I notice that the list kept by TechTV has been abandoned too. The author there finished up recommending that no attachment of any kind should ever be opened.


If you're running an old version of Microsoft Word, you need to be careful when opening Word documents. These have the extension .doc.

If you want to view file extensions in Windows Explorer, you have to go through the tedious process of changing the settings on your computer. Here are the details.


Safe procedures for email

An introduction to viruses

Assess your risk

Email and attachments

Web downloads

Anti-virus software

In Microsoft Word documents

Personal data
Mobile phones


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