Creating Zip Archives to Send E-mail Attachments

As the Internet has become more and more popular, it has also become a haven for malicious users. We at AMS Computer Services want to insure that our clients can work in a safe environment. One such attack that has become popular is to send attachments via e-mail that contain viruses, trojan, or malicious macros. In order to prevent your computer from such attack we have implemented virus filters and have further extended this to prevent certain file extensions from passing through the mail server. The file extensions are listed below:

.ade, .adp, .bas, .bat, .chm, .cmd, .com, .cpl, .crt, .eml, .exe, .hlp, .hta, .inf, .ins, .isp, .jse, .lnk, .mdb, .mde, .msc, .msi, .msp, .pcd, .reg, .scr, .sct, .shs, .url, .vbs, .vbe, .wsf, .wsh, .wsc

This list of file extensions was recommended to us by another party. You may think that the list is too aggressive, but we prefer to err on the side of caution because you never know when a virus or trojan will be spread in this manner.

How does this prevent you from infecting your computer?

This is not a foolproof method to prevent the spread of these malicious programs, but it is a start. The thinking is simple. By archiving these files into a ZIP file, the recipient is forced to think twice before executing the contents. If the recipient is intending to receive an attachment from the sender, then they will know and be able to unzip the file's contents to view the information. However, a lot of viruses are being spread where they appear to be from someone the recipient might know. If the recipient is not intendting to receive an attachment from this person, then they will have to unzip the contents to view the information. This extra step might prevent someone from performing the task and executing malicious code on their computer. An infected computer is likely to send the virus out to other computer, further spreading the code.

This guide details how to create a ZIP archive of the files you are wanting to send in the e-mail. The files do not have to be contained in a ZIP file, you can use any compression algorithm. ZIP is a popular archiving algorithm and is found on many computers, that is why it is suggested. You will need a zip archiver to be able to both compress and decompress the ZIP file. One of the most popular ZIP archivers for Windows is WinZip. You can read more about WinZip and download it at:

Creating a Zip File

To create the ZIP archive containing the file or files that you want to attach to an e-mail, you will need to find the files by navigating through your system to find the files. You can use the My Computer icon to find the files on your hard drive to add to the archive.

Winzip Image 1

In this example, I am going to send the file demo.exe so I will need to archive it. Select the file that you are wanting to attach. If you have multiple files, you can select multiple files by hold doing the Ctrl key on your keyboard while clicking the filenames. Once you have the file or files selected, click on File --> WinZip --> Add to.... The archive name will be the same as the file you are archiving, minus its file extension and replaced with a .zip extension. This is illustrated in the image below.

Winzip Image 2

After you click this button, you will notice a file with a .zip file extension in the same directory. This is the file you will want to attach to your e-mail.

Winzip Image 3

In your e-mail client when you select the file to attach, navigate your way to this directory and attach this zip file to the message.

Uncompressing a Zip File

To uncompress or decompress a zip file, you will need to save the attachment somewhere on your hard drive, and then navigate to this directory in the same manner as above, using My Computer.

When you double click on the zip file, you will open WinZip (assuming WinZip is installed on this computer). From there you will see the contents of the zip archive.

Winzip Image 4

Now click on Actions --> Extract...

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This will bring up another dialog box. Here you can select the directory that you want to extract the file to. In this example I will extrac the file in C:\Demos. You can type the path in the textbox or you can select the path with the directory structure.

Winzip Image 6

Now click Extract and the contents will be extracted to this directory. You can use My Computer to navigate your way to the directory you extracted the contents to, and you will see the file contents.

Winzip Image 7

You can now execute or read the information that was sent to you in an e-mail. It is probably a good idea to scan the files for viruses with a virus scanner before executing, just to be safe. If you have any questions or comments on this guide, feel free to use our contact form to give us feedback.