Best Free Antivirus Software


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Antivirus software provides an essential layer of protection from viruses, trojans, worms, spyware, adware, dialers, keyloggers, and rootkits. However, don't let the name antivirus confuse you. These days every good antivirus has good detection rates for all forms of malware, not just viruses. The term malware includes viruses, trojans, worms, spyware, adware, dialers, keyloggers, rootkits, and any other software which performs malicious activities on a computer.


Sadly, the amount of malware currently in circulation is so large that no antivirus could possibly detect all of it. Despite vendor's claims, no single antivirus solution can detect nearly all new malware. There are some products out there, including some in this review, which include technologies which are able to adequately protect a computer, but any product which relies mainly on detection is statistically doomed to fail eventually. Also, using more than one real-time antivirus at the same time uses much more system resources, can cause system errors, and can even reduce protection due to unintended conflicts. For my advice on how to compensate for these weakness of antivirus products please see my other article about How to Stay Safe While Online. Having a good antivirus product does go a large way towards adequately protecting your computer, but in this day I would highly recommend that you add additional layers to your security arsenal.


Below I have reviewed some of the most effective Free Antivirus products currently on the market. In order to make this review more unbiased, although I do of course admit that my own intuition and experience does affect my judgment as well, I came up with a particular methodology for comparing these products. This methodology is described in the following section.

Recent Changelog:

18-12-2015 - New article editor: Added products to be reviewed

Products to be Reviewed:
  • Avast Free Antivirus
  • Avira Free Antivirus
  • AVG Antivirus Free
  • Baidu Antivirus
  • Bitdefender Antivirus Free
  • Clearsight Antivirus
  • Comodo Internet Security Premium
  • Fortinet FortiClient
  • Nano Antivirus 
  • Panda Free Antivirus
  • Qihoo 360 Total Security
  • Roboscan Internet Security Free
  • Sophos Home Antivirus
  • Windows Defender
  • ZoneAlarm Free Antivirus + Firewall


Methodology For Comparing Products

The main motivation behind why I came up with this particular methodology for this review is that I value system protection against real world threats above all other categories by which an antivirus is commonly judged. It does not matter to me whether an antivirus protects the user by detecting malware, blocking dangerous sites, behavioral analysis, sandboxing, or any other approach. The most important thing is that at the end of the day your system is safe from infection. Thus, that is the attitude I have taken towards reviewing these products. My criteria is entirely based on protection, not cleaning. Therefore, if you believe your computer may be infected please first see my article on How to Know If Your Computer Is Infected before continuing to read the rest of this article.


I have located reputable Antivirus testing organizations which claim to test products against situations which resemble real-world situations. I narrowed these down by further requiring that the organizations have a relatively long record of producing good, seemingly unbiased, results. The organizations I ended up with, and therefore used for this review, are:



Dennis Technology Labs

From here I looked at all tests spanning back over the last two years. However, if there were more than three tests within that range I used only the most recent three. Also, if given the choice between results from different operating systems, I chose that for the most popular operating system. At the moment Windows 7 is the most popular operating system.

Also, I only considered results if it was specifically the Free Version which was tested. This is because the results for the Paid Version of the products in this review, with the exception of Comodo Antivirus (which has the exact same protection for its Free and Paid versions), are often quite different from those for the Free versions. Many marketing teams try to cloud this difference, but for the purposes of getting the most reliable information I am strict about this. Unless it can be explicitly proven that every protection mechanism is exactly identical to the free version the results for paid products are not considered in this analysis.

In addition, I did not count it against any of the products if they were not tested by multiple organizations. As long as they were tested by at least one, within the above-mentioned period, they were considered. This criteria was chosen because there are many reasons to choose not to participate in a test. Thus, it should not be held against the product if they were not tested by multiple agencies. However, if they were not tested by any, this makes it impossible to compare them in an unbiased fashion.


Once this data was collected, I then looked at the overall results for the Free Antivirus products discussed in this review, and ordered them mainly according to the quantitative results. However, my own knowledge of the products, and the reviews and experiences of others, were also considered. The results are presented and discussed below.

Discussion And Comparison

Comodo Antivirus is my top pick for advanced users, or for Intermediate users who are okay with an antivirus software which will occasionally ask them for input. However, if you do not fall into those categories, or for any other reason find it to not be a good fit for you, then you will likely find my next pick suitable. Also, for those who prefer a complete solution, there is always Comodo Internet Security (CIS), which is also free and includes a firewall in addition to all other components which already come with Comodo Antivirus.

Firstly, I will note that I am a volunteer moderator (not employee) on the Comodo forums. However, this is certainly not the reason I chose this for the number one position. The reason I made this my top pick for advanced users or users who are okay with a somewhat talkative antivirus software, is because it is the only product which I feel confident saying that it will protect you against nearly 100% of real-world threats. This is because it maintains a white-list of known safe applications. Then, all unknown applications, which include all unrecognized malware, will be sandboxed and isolated from the rest of the system. Thus, this product provides very strong protection against even zero-day malware.

Comodo Antivirus also uses the cloud to facilitate the detection of the most recent malware, as do many other Free Antiviruses reviewed in this article. It will also analyze unknown applications for suspicious behavior, and alert the user accordingly. However, as mentioned previously, users who do not want a somewhat talkative antivirus should continue to my next pick. Also, by default Comodo Antivirus has small advertisements (which can be disabled as shown here). Also, please see my notes in the Quick Selection guide for advice on how to avoid unwanted software during installation.


Panda Cloud AntivirusPanda Cloud Antivirus is an excellent choice for average users, who may find Comodo Antivirus too confusing. It has a simple interface, completely automated features, access to cloud-based protection, and has been shown to be very good at protecting a computer. Panda Cloud Antivirus has a behavioral blocker, web protection, and access to cloud-based protection, all of which will help increase your security. The protection offered by this product is very strong. However, do note that it will auto-quarantine files which it believes to be dangerous.




Avast! Free AntivirusAvast! Free Antivirus has very good protection rates. Avast has many different protection shields, boot-time scanning, a behavioral blocker, an internet site ratings plugin, script malware protection, and access to cloud-based protection. It's arguable whether their ratings plugin offers comparable levels to Web of Trust, but the script malware protection can prevent certain browser exploits, a feature not available in any of the other free AV's reviewed.

However, do note that Avast requires a free registration to function after 30 days, and the default installation installs the Chrome browser unless you uncheck it. Also, note that the OpenCandy advertising component is integrated into the Software Updater tool in Avast. More information about OpenCandy can be read here. Thus, if a user selects this option during the install they will end up with OpenCandy on their computer. My advice would be that if you want to install Avast you should not use the Software Updater tool.


AVG Anti-Virus Free EditionAVG Anti-Virus Free Edition is also a good choice for average users. My analysis of the results, as discussed in the methodology section, does show that it does a decent job of protecting your computer. However, it appears that the above Antivirus products tend to do better. Also, it comes with advertisements (but they can be disabled).





360 Total Security is also a good choice for average users. Although it has gotten some very stellar reviews, the results I found from looking at the results from the testing agencies referenced earlier in this article show that the protection it provides is roughly the same as AVG, but certainly not as effective as Comodo, Panda, or Avast. This product uses multiple antivirus engines to detect malware. It has cloud protection, and also uses the Avira and BitDefender engines, although these are not enabled by default. For more information about this antivirus, see the separate article on this page.

Avira AntiVir Personal EditionAvira AntiVir Personal Edition is another product which has a very good reputation. However, the free version was not tested by any of the three testing organizations I referenced in my methodology. Therefore, I cannot currently recommend it above any of the previously mentioned products.

However, other comparative tests do show that it has very high detection rates for malware. Also, many users have used it and found that it is very effective. Also, Avira provides access to cloud-based protection. AntiVir is certainly a good choice for a free antivirus, but due to the lack of real-world testing, at this time I cannot recommend it above the other products in this review. Hopefully in the future they will have the free version tested by these organizations as well.



Bitdefender Antivirus Free Edition

Bitdefender Antivirus Free Edition is another free antivirus product which has a very good reputation. However, the free version was not tested by any of the three testing organizations I referenced in my methodology. Therefore, I cannot recommend it above any of the previously mentioned products.

The engine for this product appears to be very similar the commercial product, although there are some tweaks. However, the level of protection provided has not been shown conclusively to be identical with the paid version, which is why I did not use the results for the paid version in my analysis. Bitdefender Free has both local and cloud-based definitions. Thus, users always have access to the most up-to-date definitions. It also has an effective heuristics engine, and uses a component called the Active Virus Control to monitor applications in real-time for suspicious behaviors. In addition it also has a webshield, which seems quite effective at protecting users from both malware infested and phishing sites.

The user interface for this product is very minimalist. Thus, it may be attractive for novice users, although more advanced users may be frustrated at the lack of customization. However, it has no offline installer, and it also requires registration to continue using it past 30 days. Bitdefender Antivirus Free Edition is a good choice for a free antivirus, but due to the lack of real-world testing, at this time I cannot recommend it above the other products in this review. Hopefully in the future they will have the free version tested by these organizations as well. Also, note that if you are having trouble getting Bitdefender Antivirus Free Edition to install in English please follow the steps in this post.


Please help us by rating this review

End-Note: Please note that I also looked into Forticlient , Kingsoft, and Microsoft Security Essentials. However, I found that the protection offered by these products is subpar. Thus, if you are considering using Forticlient or Kingsoft I would strongly recommend that you instead consider another of the products reviewed in this article.

Related Products and Links

Other Articles By Chiron

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Quick Selection Guide

Comodo Antivirus

Gizmo's Freeware award as the best product in its class!

Runs as a stand-alone program on a user's computer
This has full real-time protection capability, including real-time antivirus, behavioral blocking features, cloud-based protection, and an automatic sandboxing function which protects users from nearly all malware.
The automatic sandboxing function, although not very intrusive, may be too talkative for some users. Also, by default non-intrusive advertising is enabled (although it can easily be turned off). Also, Comodo Secure DNS, which is offered with Comodo Antivirus during installation, tends to have many false positives. Thus, I would suggest that you untick the option to Enable Comodo Secure DNS during installation.
Version 6.x
32 and 64 bit versions available
Unrestricted freeware
There is no portable version of this product available.
Take care to avoid the installation of unwanted software during installation. To do this use the customized installer button, which is on the lower left-corner of the screen during installation. Additional software, including a browser, an ad-blocking addon, and an option paid service which would allow Comodo technicians to help you with computer problems, are all included by default. Also, I would suggest that you untick the option to Enable Comodo Secure DNS during installation. It tends to falsely block many safe pages. Also, note that although the download page linked to above does not list Windows XP as being supported, Windows XP x32 is fully supported, although Windows XP x64 has significant limitations.

Avast! Free Antivirus

Runs as a stand-alone program on a user's computer
This has full real-time capabilities, behavioral blocking features, script malware protection, and a low rate of false positives.
Default settings require certain user interaction. It is bundled with Chrome browser by default, and if not carefully avoided during installation the user may accidentally install OpenCandy (see discussion for clarification).
Version 9.x
32 bit but 64 bit compatible
Feature limited freeware
There is no portable version of this product available.
Take care to avoid the default inclusion of the Chrome browser and OpenCandy during the install process by using the custom install option. The attempt to install these will also be repeated at the program update if the automatic option is chosen. Quick Start Guide: Forum:
Windows 2000, Windows XP, Windows Vista, Windows 7, Windows 8.x, Mac OS

Panda Cloud Antivirus

Combines a web service with a stand-alone program
High detection rate of malware, web protection, some behavioural blocker features
Detection rates of real-world malware is slightly lower
Version 2.x
32 and 64 bit versions available
Free for private use only
There is no portable version of this product available.
Windows XP, Windows Vista, Windows 7, Windows 8.x

AVG Anti-Virus Free

Runs as a stand-alone program on a user's computer
Behavioural blocker
Slightly lower signature detection rates
Version 2013.x
32 and 64 bit versions available
Free for private use only
There is no portable version of this product available.
Forum for support
Windows 2000, Windows XP, Windows Vista, Windows 7, Windows 8.x

360 Total Security

Runs as a stand-alone program on a user's computer
Contains many engines for malware detection.
Avira and Bitdefender engines are not enabled by default.
32 bit but 64 bit compatible
Unrestricted freeware
There is no portable version of this product available.

Bitdefender Antivirus Free Edition

Runs as a stand-alone program on a user's computer
High detection rates, very user friendly
Lack of customization, no offline installer, requires registration after first 30 days
Version 1.x
32 bit but 64 bit compatible
Free for private or educational use only
There is no portable version of this product available.

Avira AntiVir Personal Edition

Runs as a stand-alone program on a user's computer
Outstanding detection of malware
Not the most user friendly
Version 14.x
32 bit but 64 bit compatible
Free for private use only
There is no portable version of this product available.
Windows 2000, Windows XP, Windows Vista, Windows 7, Windows 8.x

This software category is maintained by volunteer editor George.J. Registered members can contact the editor with any comments or questions they might have by clicking here.


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Unfortunately, there are other Avira [Free] AV users who confronted themselves with similar situations. Volens-nolens, you received a lesson: you should have installed, on your PC, a "Backup and Disaster Recovery Software".

You can find some useful suggestions, in this respect, right here, on TechSupportAlert website:

There are other free "disk imaging" solutions, as well; provided by Macrium Software, EaseUS, Paragon Software, a.s.o.

In what concerns the AV, I would like to give you a helping hand - in the hypothesis that you are still using Windows XP:

If you have enough free time at your disposal, reinstall the Operating System. And then, if you like so much Avira's product, download and install Avira 9. You can find it at this URL:

Then you can download a valid license key, from here:

(On the above indicated webpage you have the dl. link and the updating instructions.)

Finally, if you want to update Avira's AV Free database, DO NOT use the automatic update service (in fact, I advise you to deactivate it). Always download the Virus Definition File from here:

Then proceed to Manual Update.

I understand why you like Avira AV: its resources consumption is low. And its protection is almost unbeatable. Unfortunately, starting with Avira AV 2010, this very good product began "to glide into bad habits".

But, before going back to Avira, maybe you would like to try, a little, Avast Free Antivirus 7. At least in what concerns its interface, you might remain impressed...

I hope this helps.-

Hi Wolfram
I did as you suggest but hit a problem that when I try to manually update from the fsbdev file Avira says that it cannot update as the license is no longer valid.
Do you have any suggestions as to how to get a valid license for this version as it is no longer supported?

Yes, I sure have. But I do not know if Gizmo will allow me to post a "direct download link" - for the "hbdev.key" file. Anyway, here it is:

http [ COLON ]//personal [ DOT ] avira-update [ DOT ] com/package/peclkey/win32/int/hbedv.key

If my post will be edited, here is what you can do:

In the above indicated link (, please read the post number 2 - belonging to Barrie. And follow, exactly, his instructions.

Important: you can NOT "manual update" the "hbdev.key" file! The Manual Update I was talking about it refers ONLY to the Avira Antivir Virus Definition File ( - downloadable from Softpedia.

Note: if you want to be allowed to delete the old "hbdev.key" file, you must make the following "maneuvers":

Open Avira Antivir Personal Free Antivirus main window. Then click on "Configuration". In Expert mode, click on General, expand, and select Security. Then uncheck both the options under Product Protection.

Now you can delete the old "hbdev.key". And replace it with the new one.
Your copy of Avira 9 Free should have a period of life prolonged up to 30.06.2013.

Now go back to Configuration menu, and check both the options from Product Protection. Then Re-start your machine.

And, voilà, now you have a fully functional Avira 9 AV!

I tested all these on someone else's PC and everything worked "like greased".

Good luck!

[Moderator's note : Link obfuscated. Please respect the rules of the site.]

Hi Wolfram
thanks - it worked and as you say just like the good old days - fast and clean. Just one problem the license runs out shortly - how cann it be extended if it is a non supported version now - I see the same question was asked on the forum link you provided ?

Well, I am quite sure that Avira will release a new hbedv.key file before that "expiration day". I noticed that they are doing this every six months, or so. As long as the newer versions of Avira AV will use the same old hbedv.key file, the "life" of Avira 9 will be maintained. The download link for this "vital" file will remain the same. But, I suppose you can manually update the program (its viruses definition file, I mean), even if its License has expired long time ago. I am glad that you have succeeded to set-up a fully functional machine. Try to always avoid the "Automatic Updates", if possible.-

thank you for your very helpful and well considered response.
I do have a back up system installed it is [commercial mention edited out] which whilst it is not freeware it is superb so I could get back to where I was a week or so before the Avira fiasco but of course things change in a week so I thought I could repair the system - which I did but it took some time! I could still go back to the old image but my point was the agressive way Avira behaved and how it installed and removed items without user permissions.
I did like Avira - as you say very light and pretty good detection and reasonable user control. I must say what they have done to it is needlessly agressive as well as ill thought out.
The same comments and problems apply to the paid for version if any one was thinking of trying that.
Thanks for the links to the old version and definitions updates I wasn't aware that they were available other than through automated download.
I have thought about Avast but heard some negatives abd was worried again about compatibility issues as this destroy competitors software seems to be becoming almost universal. I shall have another look given your very helpful comments.

Please consider checking out Comodo Antivirus once more. From what I've seen it's detection rates have risen drastically and the false positives have fallen. Also, it now includes a lot of very useful, and I believe user friendly, features.

Yes, plz test & review Comodo Internet Security 6, the latest version. As Chiron mentioned the detection rates have risen drastically & the FPs have fallen, I agree. Tested it quite a few times. And I find the latest CIS 6 easy, suitable & recommended for average i.e majority of users too.

As MC said, I would like to wait and see for further testing by established organisations first. Basically I aim to be very conservative in the AV category, as 1. the recommendations have to fit a large target audience of average users and 2. there are already so many established AV's that work. I'm not saying Comodo AV is necessarily bad, but not as reliable as other tried and proven AV's out there.
The editor of this category will of course make his own decisions about which products to include. It is unlikely however you will see Comodo featured until they begin to participate in more independent testing. I understand the failings of such testing (as stated by Comodo) and in the most part I agree, but even so our readers want a selection of resources to compare products with. Therefore, until we see Comodo featured on AV Comparatives, VB RAP and etc., these conditions are not met. MC - Site Manager.

Why include Microsoft Security Essentials then? It too failed to pass even 30% of the test samples. Microsoft should be lauded for including an antivirus product in Windows, because it seems that half the computers I repair have no working AV product. However, it requires a great deal of resources to just maintain the quality of an antivirus product, not to mention improvements. Although a good product at launch, it seems to have fallen off in detection precipitously. I have tested it myself on an extra PC I use for such a purpose, and it allowed half of the items Avira flagged right through...and then allowed execution of the viral losds. As a result, I have advised my clients to uninstall MSE and use Avira instead. I would prefer AVAST, but it confuses novices and makes even PCs with Core2 Quad processors seem like they are running on 1Ghz single-core Atom processors. AVAST does not cripple my PC, but then I have a 2500K, 12GB DDR3 and an SSD. Which is why I play safe and recommend AVIRA along with MALWAREBYTES or SUPERANTISPYWARE free versions.

This is why. No one amongst my own circle of MSE users has become infected over the last year and I remain confident it is an obvious and ideal choice for Windows users. MC - Site Manager.
Is it light to run?

I am running it on 3 laptops. 2 Win 7 64 & 1 XP 32. Here, light on all the 3 systems. No probs here.

Win 7 64 with 4GB RAM
XP 32 with 512MB RAM

According to them... "CIS 6 is the fastest and the least resource intensive product we have released so far". Considering it was always light in general use anyway, this should appeal to a lot of folks. MC - Site Manager.

Yes, here the previous versions were light too & so is the latest version.

Thank you both. I might have given it a try on my old PC with P-III and 512MB RAM, but sadly, 256MB of RAM got bad somehow. I don't think I would run any AV on such meager amount of RAM.
Yes, it is XP. Thanks, I might give it a try later :).