Files arrive on computers several different ways. Some are loaded as part of a software installation; others are transferred onto the computer over a network or from a removable storage device; other files are downloaded from the Internet (with or without the user’s knowledge); and other files arrive as email attachments. When a file arrives on your computer, how it arrived provides you with a clue as to its safety.
For example, if you transferred some work documents from your desktop to your laptop via a USB stick, you can be reasonably assured that the files are not dangerous. Likewise, if you transfer photo files from your digital camera to your hard drive, those files are most likely safe. On the other hand, if an email with an attachment arrives from a stranger, the file’s safety should be immediately questioned. In fact, if an unsolicited file comes from a stranger, it’s most likely some form of malware and should be removed, preferably by your antivirus program. If you must manually delete it, delete the entire email message, making sure not to open the attachment.
Your next clue as to a file’s potential for danger is its file extension. Certain file extensions are more notorious than others, especially executable file extensions such as.exe,.bat, or.com. When an executable file is clicked, an application runs. This application could be either innocent or dangerous. Again, consider the source before taking any action. Did an.exe file arrive from a trusted source? For instance, is it a software setup file that you downloaded from a site such as Microsoft.com? If so, then it’s likely safe. If the.exe file randomly arrived, it may be dangerous.
If you notice a file with the .com file extension, be especially careful. Not only is the.com file extension an executable, MS-DOS application file, it is also deceptive thanks to the use of “.com” in URLs. You may think that a file with the.com file extension is a link to a Web site, but it’s not, so use extreme care before clicking.
Another sign that a file might be dangerous is when the file has a double file extension such as filename.gif.exe. These file extensions are named with double extensions to trick users into thinking that they are safe. For example, if your computer isn’t set to display file extensions, the file with the double extension will look legitimate. In our example, filename.gif.exe would appear as filename.gif. In general,.gif files are safe to open, so a savvy computer user wouldn’t see the dangerous.exe extension and have a false sense of security when seeing the relatively safe.gif extension.
Because a file’s extension does provide you with clues, it’s smart to set up your computer to display file extensions. This is done in the Control Panel’s Folder Options. In Windows 7 and Windows Vista, go to Start and type Folder Options into the Search bar and then click on the Folder Options link once it appears. Next, click on the View tab and then remove the checkmark next to “Hide extensions for known file types.”
A final consideration when opening newly arrived files is whether you are expecting the file or not, regardless of its file extension or who sent it. For example, it’s not uncommon for malware to overtake a computer’s email system and send viruses on behalf of the computer’s owner. While you may trust your family members and coworkers not to send you infected files, you can’t always be sure that your contacts’ computers haven’t been commandeered by malware. If your boss lets you know that he’ll be sending you a report and then an email arrives with a file named “salesreport.exe,” then it’s likely safe to open because you are expecting it. On the other hand, if out of the blue an unexpected email arrives from your boss with an attachment named “funnymovie.com,” you’d be wise to ask your boss what the file is for before opening it.
Dangerous files will arrive on your computer. Whether your computer gets infected or not often starts with you making smart decisions on how to handle these files.