[HOWTO] Run a Deep Scan for Malware

What is a Deep AntiVirus Scan?

As you've noticed, the "quick scan" option is the default in almost every anti-virus and anti-malware software. A quick scan examines only the most common spyware hiding places, such as the Windows system folders, your Documents and Settings folder, and the registry.

A deep scan, sometimes referred to as a "full scan", "complete system scan", or "whole computer scan" examines every bit of your computer's RAM memory, hard drives, and removable drives. A deep scan will also scan your startup programs and the Windows registry for any traces of malware.

Malware (viruses, spyware and other nasties) usually comes in the form of an EXE or DLL file, but it can also hide in a JPG file (graphics image), a DOC file (Microsoft Word), a PDF, and many other places you wouldn't expect. If a virus or rootkit is lurking anywhere on your hard drive, external drive, flash drive, or on a CD/DVD disk, a deep scan should find it.

Because it must open and scan through every file on every drive, a full scan will take a lot longer than a quick scan. You should set aside at least two hours to allow a full system scan to complete. You can continue to work while the scan is in progress, but performance will probably take a significant hit due to the disk-intensive scanning operation.

How often should you run a full or deep scan? Most experts agree that a scheduled quick scan will do a good job of protecting you, if run on a daily basis, along with real-time malware detection. These are standard features for almost all anti-virus software, even the free versions. I would definitely recommend a full scan if you suspect that your system is infected. Beyond that, a full scan once a month seems more than sufficient. If you're paranoid, or just have CPU cycles to burn late at night, schedule a deep scan to run weekly.

How to Start a Full Scan

There are many different anti-virus programs available, so it's not always obvious how to initiate a full anti-virus scan, and which options are important. Below are step-by-step instructions for deep scanning with the most popular free anti-virus programs. Click the desktop icon or the mini-icon in the task bar to open your program's main menu, then jump to the appropriate set of instructions. If you don't have an anti-virus program yet, or you want to check into free alternatives to the paid security software you now have, see my related article on Free Anti-Virus Programs before continuing.

Avast Free - Full Scan

• On the Avast main menu: click "Protection"
• Click the "Scans" option
• Under "Full Virus Scan", click "Settings"
• Under "Scan Areas" select "All harddisks", "All removable media", "Rootkits (full scan)", and "Auto-start programs and modules loaded in memory".
• Select the "content" radio button under "Recognize file types by"
• Check the box next to "Scan all files"
• Click OK to save settings
• Click "Full Virus Scan" to run the scan.

AVG Free - Full Scan

• On the AVG main menu: click the gear icon next to the green "SCAN COMPUTER" button
• Click the gear icon next to the "Deep Scan" option
• Under "Full Virus Scan", click "Settings"
• Under "Scan Areas" select "All harddisks", "All removable media", "Rootkits (full scan)", and "Auto-start programs and modules loaded in memory".
• Select the "content" radio button under "Recognize file types by"
• Check the box next to "Scan all files"
• Click OK to save settings
• Click "Deep Scan" to run the scan.

You might have noticed that the instructions for deep scan with Avast and AVG are almost identical. That's because AVG was purchased by Avast in 2017.

Avira Free - Full Scan

• On the Avira main menu: click "Open" on the line that says "Antivirus"
• Click the "Scan" icon
• Select "Full Scan"
• Select "Start Scan"

MalwareBytes Anti-Malware - Full Scan

In addition to the full scan option in your antivirus program, I recommend that you download the free MalwareBytes Anti-Malware (MBAM) program and run the full scan option in this program as well. MBAM scans for all types of malware (not just viruses) and sometimes finds things that are not detected by other anti-virus scanners. MBAM makes it easy:

• On the MBAM main menu: click the "Scan" button
• Select the "Custom Scan" option and click the "Configure Scan" button.
• Under "Custom Scan" options check all the boxes
• Select the disk drive(s) you want to scan.
• Click "Scan Now" to start the scan

Windows Defender Offline - Full Scan

If you are not able to start your computer due to a malware infection, the Windows Defender Offline (WDO) is a stand-alone deep scan utility that runs from a bootable CD or USB flash drive. You can also use WDO as an adjunct to the full scan option of your installed anti-virus software.

Too Much of a Good Thing

Let me repeat a caution here that I've mentioned before. It's okay to run a dedicated anti-virus program along with an on-demand scanner such as MBAM. But I strongly advise that you run only ONE dedicated anti-virus program at a time. If you run two or more, the real-time virus detection engines can actually fight with each other. Each will think the other is an attacking virus, and the ensuing battle for supremacy can bring your system to a crawl.

I actually tested this once on a Windows 7 system. After installing Microsoft Security Essentials, Avira, and Avast, my system came to what seemed like a complete halt. I hit the power button to reboot, and 20 minutes later it was still cranking away. Trying to open any program or navigate the web was like swimming in wet cement. If you want to install a second antivirus program to run a "second look" scan, be sure to use the option to disable real-time protection in the first one.

Do you have something to say about running a deep antivirus scan? Post your comment or question below...