How to Run a Deep AntiVirus Scan

Category: Anti-Virus

My anti-virus software offers me the option to run a quick scan or a full scan. I've always run the quick scan, because that's the recommended setting. What does a full scan do, and how would I know if I need to do one?

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" or "complete system scan" examines every bit of your computer's RAM memory, hard drives, and removable drives.

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 is lurking anywhere on your hard drive, external drive, flash drive, or on a CD/DVD disk, a deep scan should find it.
Antivirus Deep Scan

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.

AVG Free - Full Scan

  • On the AVG main menu: under "Scan Now", click Scan Options
  • Under "Whole computer scan", click "Change scan settings"
  • Check all boxes
  • Click "Additional scan settings"
  • Under File types for scanning, select "All file types"
  • Check "Scan files without extensions", then click OK
  • Click "Start Scan" button
  • Click "Stop" to cancel a running scan. You won't hurt anything, just scan again later if desired.

Avira Free - Full Scan

  • On the Avira main menu: click "Local Protection"
  • Right-click "Complete System Scan"
  • Select "Start Scan (admin)"
  • Click OK on the security popup
  • Right-click "Scan for Rootkits and active malware"
  • Click OK on the security popup
  • Select Start Scan (admin)

Avast Free - Full Scan

  • On the Avast main menu: click "Scan Computer"
  • To the right of "Full System Scan", click "More Details"
  • Click "Settings" then click "Sensitivity"
  • Select "Test whole files" and "Scan for potentially unwanted programs"
  • Click OK to save settings
  • Click Start to run the scan.
  • If desired, run the "Removable media scan" with the same settings.

Microsoft Security Essentials - Full Scan

  • On the MSE main menu: select the "Full" radio button
  • Click "Settings" tab, click "Advanced", then select these options:
    • Scan archive files
    • Scan removable drives
    • Create a system restore point
  • Save changes, return to the Home tab, and click "Scan Now"

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 dedicated anti-virus scanners. MBAM makes it easy:

  • On the MBAM main menu: select the "Perform full scan" radio button
  • Press the "Scan" button.
  • Select the disk drive(s) you want to scan.
  • Click OK to start the scan

Microsoft System Sweeper - Full Scan

If you are not able to start your computer due to a malware infection, the Microsoft System Sweeper (MSS) is a stand-alone deep scan utility that runs from a bootable CD. You can also use MSS as an adjunct to the full scan option of your installed anti-virus software. System Sweeper uses the same "engine" as Microsoft Security Essentials, so if you've already done a deep scan with MSE, there's no reason to use MSS.

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 just tested this on my new Windows 7 laptop. After installing Microsoft Security Essential, 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. Try to open any program or navigate the web was like swimming in wet cement.

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Posted by on 27 Sep 2011

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Most recent comments on "How to Run a Deep AntiVirus Scan"

Posted by:

27 Sep 2011

There's an awful lot of work in preparing these individual, step-by-step instructions, but this is one of the very most important posts Bob could make. Follow these instructions faithfully and your chances of your computer surviving will be enhanced greatly. Thanks, Bob, for a great post.

Posted by:

27 Sep 2011

Hi, Bob. Is there any reason (I mean will I get any better results) if I run a full scan in fail-safe mode?

EDITOR'S NOTE: Not sure what you mean by "fail-safe mode". Do you mean starting the computer in Safe Mode? If so, I don't think that would offer any additional benefit.

Posted by:

27 Sep 2011

Hi Bob, Thanks for a great article. I've been a fan of yours for years now. Because of your teachings, people think I've been well educated in computers. I've helped a lot of my friends and family repair their computers and save their money from expensive repair shops. One problem i've always had is when they ask for instructions on how to use these security programs. With this article, my problem is solved. I just need one for superantispyware which I can now create following the examples you have above.

I have told many people to go to your website before they send in their computer for an expensive repair. From my experience, following your instructions is a lot more effective than sending computers in for repair by technicians who have never successfuly gotten the job done (yet still charged me a hefty fee). The world needs more people like you Bob. Your integrity can't be outmatched. Keep up the great work!!!

Posted by:

28 Sep 2011

Hello Bob, I ran a deep scan on Avast Free a few months ago and as you said it took well over an hour and it came up with all sorts of so called infections which turned out to be false positives.It also suggested running a boot time scan which I accepted. This turned out to be a very bad move because when I next turned the computer on it would not boot up onto the C drive.Luckily I have a dual boot system and by using the other drive I was able to sort the problem out.
Needless to say,I have not run a boot scan since.

Posted by:

29 Sep 2011

This is an FYI to Tom who posted "This turned out to be a very bad move because when I next turned the computer on it would not boot up onto the C drive." This was in reply to the How To Run a Deep Antivirus Scan, article.

In case no one else told Tom, yet, I want to let him know that his AV program was doing exactly what it was supposed to be doing. Boot Time means the time that the system is loading those things that it needs to "talk" to all of the other components that make up your computer system. It loads those programs first, then it loads the Operating System, for instance Microsoft 7 for a PC user. A boot time scan cannot take place when the OS is in use, as it can't access the programs that it uses to start up all of the gadgets, pieces and parts that make your OS able to do things like show graphics, play sounds, acknowledge a DVD has been inserted, and make use of other internal components that you would never be aware of.

A few minutes at most is all that most computers need to run the boot scan. If any Malware was found, your AV program would advise you via its notification software device. Usually, you just get a message that the boot scan is complete and then a notice telling you that it will now proceed to allow your OS to be loaded, in your case that is apparently on the C drive.

I am sure that Bob could do a more concise job of describing these events, but I thought that some one should let you know that you had not in fact let the AV program do its job. And, that your concern was simply a lack of knowledge about what Boot Time is.

Kudos to you, Tom, for applying the very good (and well written)advise found here on Bob's web pages.


Posted by:

dave sykes
22 Mar 2012

great info,have run speed up my pc and am really pleased with the pc is much much now doing full scans.i have malware bytes running now.and have set avast to run one later today.very useful info.thanks.

Posted by:

gary gross
09 May 2012

Reinstalled XP with additional sp3 cd. By the book. XP Just does not clean install without something malfunctioning. Then its DELL Driver Download,etc. Anyway, system ran super poorly after loading toolbars. Bing for my daily art fix. Norton for the protection. Chrome for the brains. Ran norton,norman,eset,superantispy,mbam,sophos,rootkit revealer,ccleaner, Iobit full scan, micro. malicious software removal tool,just in case. All with norton 360 as main antivirus provider. Found trojan,adware,cookies,rootkit,malware phew!! The worst I've ever see, for me. Note: where possible, ran programs in safe mode too! Result,everything gone! Curser flashes as perfect instead of insanely. VERY IMPORTANT: After each, used FREE REVO UNINSTALLER PRO (ABSOLUTELY MY FAVORITE PROGRAM). easy to use with no accidental removals. LEARNED ABOUT ALL OF THESE FROM "SUPER BOB RANKIN". Thanks Bob! garyog3

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