How can I tell if I have an attachment, and how do I open it?

If you're using most of the common email software programs, such as Outlook, Outlook Express and Eudora, or the common Web-based email programs such as Hotmail www.hotmail.com, the process of telling whether an email you've received has a file attached to it is similar.

In the list of new emails you've received, look to see if there's a small icon similar to a paperclip somewhere in the heading, usually next to the sender's name.

To open the file with software programs, simply double click the message with your mouse to open up the message. You will see the file embedded somewhere in your message, depending on what email system you're using. It may be down the bottom of the email, or it may be in an extra field called "Attachments". To open it, you have to double click it.

What if I can't open an attachment?

One of the main problems with email attachments is that not everyone has access to the same software. It can be frustrating when a friend emails you a file with an extension that you don't recognise and which you can't coax your PC to open.

In most cases you can choose from a range of programs to open specific file types. For example, graphic and image files use standard formats (such as .jpg and .gif), and most image or graphic software (including the ones automatically installed in most PCs running Windows and Macs) will open all common file formats.

However, with some software you can only open or view the file using the same software it was created with. For example, if a colleague sends you a Microsoft PowerPoint file, you would need Microsoft PowerPoint installed on your PC to open and view the file.

Microsoft seems to be aware of this problem, and now offers a range "viewers" for its popular software, so you can view a file sent to you in one of its formats - but the viewers do not allow you to edit or amend the files. You can download the viewers from office.microsoft.com/Assistance/9798/viewerscvt.aspx.

What is an extension?

The extension is one or several letters at the end of a filename, for example, if you have your resume saved as a Word document and you've called it resume.doc, then the file extension is "doc".

The Most Common File Types and the Software You'll Need to Open Them

Compressed files

Most of us still connect to the Internet via a modem. Downloading large files sent as attachments can be painfully slow. To speed the process up, many people "compress" files before sending them, using special software. The compression process can often result in files that are a fraction of their original size (for example, Microsoft Word files can be shrunk by up to 90%).

If you receive a compressed file, you need to decompress the file, so that it can be accessed. To do this you need the same type of compression software used to compress the file. Two of the most popular types of compression programs are WinZip www.winzip.com and PKZip www.pkware.com. These programs usually create files with a .zip extension (by far the most common type of compressed file), but they are also able to open other compressed file formats.

So if you receive a file you can't open and it has a Zip extension, you'll have to visit www.winzip.com and click on the "Download" link to get this special software on your computer. Once you've downloaded and installed that file as you usually do, you should then be able to open this zipped attachment.

Many modern viruses now have the ability to send copies of themselves as email attachments. Here's how they use the attachment function to "trick" individuals to infect their own PC with a virus:

Having infected Bob's PC, a virus embedded in an email searches the PC and compiles a list of all the email addresses it can find (mostly from Bob's email address book). It then composes and sends an email message to each address, including a "fake" email message and sending a copy of itself as an attachment.

Bob's friends receive what appears to be a friendly email from Bob with an attachment, which they naturally open, thinking Bob has emailed it because he feels they will find it of interest. Oddly, nothing happens. The friends shrug their shoulders and move onto the next email. Behind the scenes, the virus has infected a new PC and starts the process again.

A virus can use almost all types of files as an infected attachment. However, the most common types of infected attachments are those files with the following extensions:

• .bat
• .com
• .dll
• .exe
• .hlp
• .ini
• .scr
• .sys
• .vb
• .vbs

The virus won't run and infect your computer unless you open it up and double click it, however we also highly recommend getting some sort of anti-virus software on your computer such as Norton www.symantec.com/region/au_nz/ or McAfee www.mcafee.com - you can't rely on your own vigilance alone.

Another sign that the email may be a virus is if the text of the email is misspelled and perhaps isn't in the same style as your friend normally writes.

As an added precaution, if you do receive an unexpected email attachment, contact the sender to clarify that they did in fact send it to you.

By default, many Windows applications do not display file extensions, aiding viruses in their subterfuge. To turn the display of file extensions on:

1. Launch Windows Explorer (usually under Start/Programs/Windows Explorer)
2. Click on the Tools pull-down menu in the toolbar at the top of the screen
3. Select Folder Options.
4. Click the View tab.
5. Put a check in the box or circle next to "Show all files" (or "Show hidden files and folders" in Windows 2000/XP)
6. Uncheck "Hide file extensions for known file types" by clicking on it (the check should disappear).