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Best Free Antivirus: Windows Defender and 5 free alternatives



Antivirus doesn't have to cost the Earth: we have five free alternatives to paid-for antivirus in our brand-new guide.

Even if you consider yourself to be a responsible web user, you should be using security software. Thanks to the proliferation of contaminated advertising iframes, opportunistic malware-laden spam and drive-by downloads that can affect even the most legitimate, upstanding and popular of websites, nobody is completely safe.

However, expensive anti-virus suites aren't your only option if you want to stay protected. While these paid-for packages often include a wealth of useful extra features, the core protection – real-time and on-demand virus blocking and scanning – is offered by their free counterparts too.

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Windows 10 comes with Windows Defender anti-virus already installed, and we've included it in our group test as a point of comparison for all the other software on review. While paid-for anti-virus software is beyond the scope of this group test, we hope to provide you with the information you'll need to make an informed assessment on whether or not a pre-installed commercial package, such as those often bundled with laptops, will be more or less effective than its free competitors.

Detection engines

The key part of any anti-virus software is its detection engine, which uses a combination of a database of known threats and analysis of an unknown program’s behaviour, known as “heuristic analysis”.

Detection engines are at the core of most anti-virus companies' business, and you'll generally find that a company's free products use the same engines as their paid-for products, although the latter may be equipped with additional features, such as firewalls and system optimisation tools that boosts performance further.

Some companies license their engines to others. For example, in this group test, Qihoo 360 Total Security can optionally use both Bitdefender and Avira's scanning engines in addition to its own. Multiple scanning engines, whether licensed or produced in-house, typically increase the likelihood that an anti-virus product will successfully pick up anything nasty trying to attack your system. However, it’s also very likely to slow down your PC due to the sheer number of engines running at once.

Similarly, while most software defaults to an optimised scan mode that checks the files most likely to have been compromised, running a more thorough scan will take longer but might find infected files that would have otherwise gone unnoticed. Running a deep scan on a semi-regular basis would be sensible.

Testing & performance

In this group test, we've relied on results produced by the respected AV-TEST security lab to assess the performance of each anti-virus program in correctly identifying malicious files and websites and avoid false positive detections of benign software as malicious. AV-TEST also assessed the impact of anti-virus software on system performance.

We've used test data on a per-engine basis, rather than an identical product basis. So, for example, we've used results from AVG Internet Security 2016 to help draw conclusions about the AVG Free 2016 – which uses the same engine – and used other test resources to confirm comparative performance. We’ve therefore had to make assumptions that the free and paid-for versions use identical engines, but given most paid-for software simply adds extra features instead of a whole new engine, this is a reasonably safe assumption to make.

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The test data we've published was collected by AV-TEST during March and April 2016, using the most up-to-date versions of the anti-virus software available. AV-TEST carries out both real-world testing, in which systems are exposed to live contaminated websites and emails, and reference-set tests, in which several thousand malicious files collected in the previous four weeks are introduced to the system.

This time around, the software was exposed to 164 live malware attacks and 22,795 reference samples. AV-TEST publishes percentage scores showing how effectively each anti-virus suite performed in these tests, which are then used to produce a score out of six based on how successful the software was at defending a system compared to the industry average.

We'll directly quote the percentage of malware successfully defended against. It's worth noting that there can be fairly dramatic performance differences from month to month. This depends on a given anti-virus package's ability to detect the malware that's prevalent at any given point, and the speed with which its signature database and heuristic detection rules are updated to reflect current malware. Our ratings therefore reflect a suite’s recent form, which may not be representative of future performance.

AV-TEST's performance tests time the impact of different anti-virus suites on a number of common desktop tasks, such as downloading and installing applications, launching programs, copying files and visiting popular websites. Once again, AV-TEST publishes percentile scores indicating how much of an impact on performance each program has, and produces an overall score in relation to the average performance of all anti-malware suites. We'll quote this overall score and draw out any particularly interesting performance elements.

Finally, usability tests assess how many false-positive incidents each program produces when tested against 41 popular programs being installed, hundreds of legitimate websites visited, and more than a million examples of already-installed legitimate software and files.

You can see AV-TEST’s raw data on its website and draw your own conclusions if you’d prefer (Excel spreadsheet).

The price of free anti-virus

While you don't have to hand over any cash to use free anti-virus software, you can bet your bottom dollar the company that markets it is making money somehow. This manifests itself in a number of ways. Some products, including Avira and Qihoo, show unobtrusive adverts, while others are paid to bundle software from other companies, which might sneak onto your PC if you’re not paying attention during the installation process.

Any product that's available in paid-for, as well as free, versions, will encourage you to upgrade with varying degrees of persistence, with some including buttons for features that are active only for paid users in their main interface.

Some free AV software, such as Avast, requires you to register, even if you're only using their free incarnation, while others strongly encourage you to do so by providing online monitoring tools that you can use to manage and secure other devices associated with the same account – phones and tablets, for example.

Our reviews detail any obtrusive advertising or promotional features in each free anti-virus suite and, where possible, tell you how to avoid them.

Anti-virus software also reports back to its manufacturer by default when it encounters unknown malicious and even benign files. This means that the databases it relies on are kept constantly up to date, helping to protect all its users and making both paid-for and free versions of the software more accurate.


June 11, 2015, 7:48 pm

What, no BitDefender? That's my favourite free antivirus at the moment.


July 23, 2015, 12:36 am

I would have agreed with the AVG review yesterday, but today AVG, without my knowledge or permission installed "AVG WebTuneup" and made changes to my browser settings. Essentially AVG is using the same tactics as malware. I am not saying AVG is malware, but by bundling software that I did not request -- sounds like malware, too me.
Avoid AVG simply because of this practice.

Dead Words

September 10, 2015, 8:36 pm

Agreed. Subtle and effective.


September 11, 2015, 7:53 am

Is BitDefender Free compatible with Windows 10?

On a sidenote, what I like about Avast is that you can choose to use it in Silent Mode, and do away with all the popups proposing upgrades, mobile protection and the like. Important alerts are still on in that case, of course.

Dead Words

September 11, 2015, 11:16 am

Yes it is.
Bitdefender is always in that mode. It's never in your face asking for attention. When you open it, it shows up as a small window in the bottom right corner that you can close just by clicking outside the window. It never bugs you about upgrades and such and will never bother you unless it finds a problem, where it automatically quarantines it until you decide what to do with it.


September 11, 2015, 12:19 pm

I love Bitdefender but my only issue with it is the requirement for an account login. Through normal use I've seen no benefit from this and it makes it a pain when 'fixing' family PCs and installing it for them.


September 11, 2015, 1:14 pm

Is there a real-time protection in the free version as well, or just the paid version (paint me cheap...)?

I visited their website, but I couldn't ascertain this point, and it's a must-have in the world we live in.

Dead Words

September 11, 2015, 8:41 pm

Haha yes it has real-time protection and conducts scans every hour or so to see if you let anything through, and deep scans once a week.
Make sure you're getting a proper version though and not from some fad site. One of the most common ways people get crap on your computer is disguising it as protection from crap.

Dead Words

September 11, 2015, 8:41 pm

I agree. That's my only issue. You don't do anything with the account it just wants you to have one. At least it's not like Norton's account which claims to be useful but doesn't do crap.


September 13, 2015, 7:29 am

I've used Avira on and off for a number of years. I still find it confusing and not at all intuitive. Also there are nag screens, reminding you to upgrade. For the last few months I've been using Baidu free antivirus and rather enjoy it. I believe it uses the Avira engine, but not sure. Works well for me and has a host of interesting features.


October 31, 2015, 1:45 pm

Avira is great, but you if you want to get rid of nag screens, adding ipmgui.exe to forbidden Windows firewall rules is an option. Hopefully, permanent. Time will tell. All other approaches - adjusting ipmgui.exe's ACLs, preventing execution, adding to Avira's own quarantine - have failed because Avira updates ipmgui.exe from time to time. But Avira does not touch Windows firewall.


November 5, 2015, 9:24 pm

Agreed. I really didn't like how it felt. Click bait after click bait and additional software that I didn't want.
360 has good reviews, will try instead.
Had Avira before, except for nag pop-ups and a few BSODs, it was very decent.

Belén Cebrián

November 15, 2015, 5:11 pm

That's what I'm thinking to do, but with Avast! instead. Yeah, it might be better than Windows Defender, but it also tries to install aditional stuff even when you choose not to let it do it. Just now, before opening Firefox, it tried to install a plugin called "Avast SafePrice". Come on! I think I will stick with Windows Defender or try BitDefender...


November 28, 2015, 2:34 pm

I'm reading your comment because Avast just tried to install Avast Safeprice on my computer without my permission - I didn't even know of its existence until another AV program (Winpatrol, I think) informed me Avast was trying to install it.
I'm done with Avast. It's gotten extremely intrusive lately and some of the messages imply I need to upgrade when that's clearly not the case. When I got a computer with Win 8, Avira Free wouldn't run with it and I switched to Avast. I'm guessing Avira works now over a year later and with Win 10.


November 28, 2015, 2:37 pm

Windows Defender protects against 77% of viruses and Avira and Avast in the upper 90%'s. I wouldn't trust Windows Defender at all.


December 11, 2015, 5:07 pm

I just had a windows upgrade and my Bitdefender stopped working. It is incompatible with the latest update of Windows 10. Unfortunately, I paid for the Bitdefender and my licence is still on.

Dead Words

December 11, 2015, 10:01 pm

My Bitdefender works perfectly fine and I've been a Windows Insider for a real long time now so I'm always running the latest Windows 10 Build.


December 11, 2015, 10:41 pm

My update was yesterday (Dec. 10, 2015). So, if you have an idea why the computer is saying my BD cannot run on the current update, let me know.

Dead Words

December 12, 2015, 4:04 am

Sounds like it was the cumulative update (Build 10586.29) that was also released for Windows 10 Mobile. It's predominantly bug fixes and general improvements (nothing visual) and also brought some fixes to Internet Explorer and Microsoft Edge. I suggest opening Bitdefender (I'm not sure what version you have) and checking your Logs to make sure Bitdefender has been updated to the latest virus signatures. Anti-virus programs like Bitdefender and Windows Defender (really any good, decent anti-virus program) updates practically every day. Also, go to Bitdefender's site (there should be a link directly from your Bitdefender program) and ask customer service if it could be a driver issue or a confliction with Windows Defender or Windows Update (it happens occasionally, which is why Microsoft suggests temporarily turning off third-party anti-virus software before large updates).


December 12, 2015, 11:17 pm

This is a super annoying part of all free antivirus. Make sure when it is updating to decline anything that you are allowed to decline. They make you think you're accepting the terms and conditions but really you're accepting this extra garbage you don't want. They'll even first make you accept terms and then show the extra screens to make you think they are additional terms of AVG...


December 17, 2015, 10:49 pm

The latest Avast inserts ads in your outgoing email as a default option (without permission). I discovered this after the fact. It also damages my ability to send emails at various time. This was on a work email address on Google apps which Avast made look like ad-supported freeware. This is the worst I have seen yet damaging reputations of the organization I work for as well as Google and of course itself. Avast now deserves to be treated like the malware it has turned itself into.


December 20, 2015, 7:49 pm

All these free antivirus programs are coming bloated anymore. Avast and AVG also. I'm sick of it, as I don't want bloat, and I don't want the antivirus program checking every website I visit. It all adds up to a ton of lag and popups.


December 20, 2015, 7:51 pm

There is also the stupid antivirus program which auto delete or lock any file it doesn't like. Its so annoying. The last time I tried uninstalling Avast it trashed my computer and I lost many files.


December 26, 2015, 1:49 pm

I have installed avast on my computers for many years and on ones I have worked on ... after installing and making sure the right boxes are unchecked i have had no problem with it and it doesn't remind me about registering till maybe two weeks before it ends. I don't get any nag screens to upgrade either. and any reminders come up at the right hand corner and after a few seconds disappear...You have to set it up right and if you don't want any ads then buy the full version... you are getting it free ..... besides being able to hook to another computer miles or states away and helping the person is a good plus for me


December 27, 2015, 4:39 am

"It does no fingerprinting of files we could see, though"
I consider that a negative for Avira, and a huge plus to AVG.

I think these reviews also need to take into account how much nagware/spam is in the software and rate that also.

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