How to Tell If a File Is Infected Before You Open It

You weren’t expecting the email attachment you just received. Or a website is asking you to install software you don’t recognize. Or a friend whose computer is infected hands you a flash drive with a file he wants you to open. Your instincts are right: If you are unsure about a file, don’t download it or open it before you do some detective work. It takes less time to check a suspicious file than it does to clean up the contamination it can cause. This guide shows you the steps to take to protect yourself.

Rely on Your Software

Your security software (antivirus or anti-malware program) most likely has the ability to check a file before you open it (or even before you transfer it from physical media to your computer). Here’s how to do it:

1. View the file’s icon in a window.

2. Right-click the icon to bring up a contextual menu.

3. Your security software may have a menu entry labeled Scan file or something similar. Click the entry to initiate a scan.

If your security software does not provide a contextual menu option, open the security software’s control panel and navigate to the scan section. Here, you will be able to select specific targets (files) to scan (sometimes this option is listed in an Advanced Options menu).

Internet Research

In cases where you aren’t able to scan a suspect file with your security software-when a website is trying to install something, for instance-follow these steps:

1. Gather as many details as you can about the suspicious software. Record the name of the software as well as the name of the website you were on when it popped up.

2. Search the Internet for the name of the software first. The legitimacy and safety of the software will usually become apparent after you read the first few results. If it is still unclear, search again for the name and add terms like “malware,” “safe,” or “remove.” Also check the reputation of the website that asked you to accept the software. If you remain unsure, stay away.

Keep Software Updated

1. The latest versions of Web browsers are able to screen downloads, warn you of harmful programs, and block recently discovered malware.

2. Most email programs scan attachments for infections before you download them. Pay attention to these scans.