Purdue University College of Liberal Arts

Information Technology

Viruses and E-Mail Attachments

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These files are probably safe

Although viruses can and do spread within data files (macro viruses, notably), our experience suggests that they have less potential for significant system-wide damage. Install an anti-virus utility; open attachments of these formats only if you know the exact purpose of the file and recognize the sender.

Data file formats can be identified by the filename suffix, or "extension," which is usually three characters long. Although it is not possible to provide a comprehensive list, here are a few common filename extensions and the programs used to read and write such files:

.doc - Microsoft Word
.xls - Microsoft Excel
.ppt - Microsoft Powerpoint
.mdb - Microsoft Access
.pub - Microsoft Publisher
.pmd - Adobe Pagemaker
.pdf - Adobe Acrobat

Some additional common filename extensions:

.jpg - photograph
.gif - graphic
.mov - movie
.mpg - movie
.htm and .html - web page

But be wary of these

Executable programs are designed to do specific tasks -- your word processor is an executable program designed for the input and formatting of text, for example. Because we can't determine a program's function from its name alone, it is inadvisable to open an executable file received as an attachment. Such files may have the following extensions:

.exe - executable file
.com - executable file
.vbs - Visual Basic script
.pif - DOS program file
.bat - DOS batch file
.zip - file archive

Virus hoaxes also arrive via email

Virus hoaxes -- false warnings about computer viruses -- have been causing unnecessary panic for years. Some hoaxes claim that merely opening certain e-mail messages will infect your computer.

Although it is highly unlikely that a virus could activate by merely opening an e-mail message, it is very possible to activate a virus by opening a file that is attached to an e-mail message.
We recommend that you do not open files received as e-mail attachments unless you know the exact purpose of the attachment. It is not enough that you may recognize the sender's name.

Here's why. Some real viruses that we've seen on campus have been designed to look in one's e-mail address book and, without the sender's knowledge, to send messages in his/her name that include an virulent attachment. The recipient, who recognizes the sender's name, thinks the attachment is fine and opens it -- which activates the virus.

If, in fact, you are expecting a colleague to send a file such as a Word document (which typically has a filename with a .doc suffix, or "extension") or an Excel spreadsheet (.xls) to you as an e-mail attachment, it is likely safe to open it.

But you should not open any executable file (.exe, .vbs, .pif, .com, and .bat are examples) or any other kind of file that you don't recognize, even if you recognize the sender's name.

Sending e-mail attachments

The corollary guideline is that you should send only e-mail attachments that have clear filenames with proper extensions, the three character suffix which identifies the file type. (See the sidebars, right.) Further, you should send them only to recipients who are expecting you to send attachments to them. Please do not send executable programs of uncertain origin. (In fact, anti-virus software on the e-mail server may prevent the transmission of executable programs as attachments.)

Macintosh users who wish to attach files to e-mail messages should add extensions to filenames before sending. In Mac operating systems prior to Mac OS X, filename extensions were generally not necessary or used. It helps Windows and Mac users alike to change, for example, a Word file's name from "Chapter3" to "Chapter3.doc" before attaching it to a message.

Consider refraining from sending frivolous attachments intended only for amusement, such as .mpg and .mov video clips and .jpgand .gif picture files. Although usually innocuous, these files may serve only to make your recipients wonder if they've received a virus via e-mail. They also consume our computer systems' limited storage space.

These simple precautions may help to prevent the spread of computer viruses.

Anti-virus software

An essential defense is to have up-to-date anti-virus software installed on every computer you use, both in the office and at home. Contact your department's computing support staff for information about obtaining software.



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