Some of our readers asked us to test the most popular free antivirus scanners found online. Since such scanners are useful in providing a good second opinion, without having to install a fully-featured security product, we thought it is worthwhile to evaluate such products. We've tested the 10 most popular online security scanners and, although it took quite a bit of work, we now have some exciting results to share with you. Don't hesitate to read this article and find which are about the best free online antivirus scanners for Windows:

The online antivirus scanners being tested

To choose the products included in this test, we used the finalists of our Digital Citizen Awards 2016 - The best Windows security product of the year!. For all the vendors, we searched to see if they also offer a free online security scanner. Unfortunately, not all of them do, and out of those who do, not all of them are good.

The products we ended up including in this comparison are, alphabetically ordered, the following: Bitdefender QuickScan , Comodo Cloud Antivirus , ESET Online Scanner , F-Secure Online Scanner , Kaspersky Security Scan , McAfee Security Scan Plus , Norton Security Scan , Panda Cloud Cleaner and Trend Micro HouseCall.

We quickly learned that many products are no longer classic online scanners which you can run in your web browser. The majority of security vendors now offer standalone antivirus scanners which you need to download and install on your computer. They can run alongside your other security products, without causing conflicts or performance issues. They can be used whenever you need them to provide you with a quick second opinion about your system's security status.

Important note: This test does not include any full fledged security product. It is about free tools that you can use to scan and evaluate the security of your system. These tools cannot and should not replace proper security solutions such as antivirus, antispyware and firewall solutions. They should be used only to complement a real security product or to help you identify what's wrong with a system which you suspect of having problems with malware.

This is how we tested these online security scanners

First, we recorded how each product is designed: if it is a true online scanner, a standalone application or a hybrid between the two. Before installing and/or running each of the free online security scanners, we ran several malware samples to infect our test system. Then, we browsed several dodgy websites that store cookies which you don't want to have on your computer, or which try to install different forms of dodgy toolbars or malware on your computer.

Once we were sure we had a few malware samples running on our system and several infected files being stored, we started using each antivirus scanner, one by one. We tested how fast they scanned the system, recorded how many malware samples they detected, what information was provided and the solutions they proposed. The scans were made on a 20GB partition with 17GB of occupied space. We used Windows 10, with Windows Defender disabled and there were exactly 17 malware samples running on our test system.

Bitdefender QuickScan

Bitdefender QuickScan is one of the few true online scanners. However, you should know that you can not run it from any web browser, as only Internet Explorer, Mozilla Firefox and Google Chrome are supported. The good thing about Bitdefender's QuickScan is that it's very fast: it took less than a minute for it to scan the computer for malware .

Unfortunately though, Bitdefender QuickScan only tells if the system is infected or not and shares the name of the first virus found active. There's no other useful information being displayed and the only option you have is to download and install a 3 months trial of Bitdefender Internet Security , so that you can disinfect your system.

While this tool is quick and painless, it doesn't provide much value to its users. There are better alternatives provided by other security vendors.

Comodo Cloud Antivirus

Comodo Cloud Antivirus is an online scanner which, like many others, comes as a standalone program that you download and install on your Windows computer. The first thing that you will notice is the fact that this scanner looks more like a full antivirus solution than just an online antivirus scanner destined to be used only casually. Its user interface offers plenty of settings and options and it's one of the few online antiviruses that we've tested which lets you run both quick and full system scans, as well as custom scans.

The quick scan we ran with Comodo Cloud Antivirus took less than 2 minutes and ended up with only one malware sample detected. This is not a very good result, but it got better in the full system scan we ran afterwards. This time, even if it took 59 minutes for it to do so, Comodo Cloud Antivirus managed to identify 13 malware samples out of the 17 we placed on the test computer.

Comodo Cloud Antivirus is one of the few antivirus scanners that are also able to clean the malware they find. And this is something worth appreciating.

ESET Online Scanner

ESET Online Scanner is one of the few very good online antivirus scanners available. ESET Online Scanner is available as a standalone Windows app that you download and run on your computer. B efore a scan is performed, ESET automatically downloads the latest signatures to your computer and it lets you customize the antivirus scan it will run. By default, ESET Online Scanner is set to scan everything on your computer: the Operating memory , the Autostart locations and the Local drives. You can also tell ESET Online Scanner whether you want it to automatically clean the threats it finds, if it should scan inside archives or not, or if you want it to scan for potentially unwanted applications.

The full system scan we ran took about 29 minutes and identified all the 17 malware samples we had on our test computer. For each identified threat, ESET Online Scanner displayed the name and the file's location. We appreciated that, after the antivirus scan ends, you can set the scanner to uninstall its own files from your computer.

ESET's security products are promoted in a discreet and non-intrusive way. ESET Online Scanner offers what you would expect from a good online scanner and we are very happy with how it performed.

F-Secure Online Scanner

F-Secure Online Scanner is another standalone program which you must download and run on your computer . Before a scan is made, it automatically downloads the latest signature files.

Then, F-Secure Online Scanner automatically starts scanning your system for malware. You can't customize anything and you can't choose what type of antivirus scan you want to run. All is automatic.

If F-Secure Online Scanner finds infected files, it will ask you to restart your computer in order for it to be able to clean them. If you want, you can also see the details about where malware files were found on your computer, how many files are infected with a certain virus and, if you're really curious, you can also go online and see more information about it.

F-Secure Online Scanner was one of the fastest antivirus scanners we've tested: it took it less than a minute to scan the 20GB partition and it managed to identify 12 malicious files, out of the 17 viruses we had running on the test computer.

Kaspersky Security Scan

Kaspersky Security Scan is another online antivirus scanner that comes as a standalone application, which you need to download and run on your computer. The user interface is simple and easy to use, and it lets you perform a quick or a full system scan and even set a schedule for regular scans. By default, the tool scans your system twice a week. Unfortunately, you cannot change the frequency, although you can change the days of the week in which they are run.

A quick scan finished in about 2 minutes and revealed only 2 malware samples. A full system scan finished in 52 minutes and identified 9 malware samples.

When presented with the results, they are split into several sections:

• Malware - shows all the infected files that were discovered during the scan.
• System protection - shows whether you have an active antivirus installed on your computer.
• Other issues - displays issues with how Windows Explorer or Internet Explorer are configured.

Everything is fine and dandy but, if you want to clean the infected files from your system, or if you want to correct any of the other issues found by Kaspersky Security Scan , you will have to go online to Kaspersky's website and download a trial or purchase one of their security products.

Go to the next page of this article to learn more about other security products, as well as our final verdict about the best online antivirus scanner.