If you have a Windows computer, you need anti-virus software. There always will be those who will insist that every virus attack is caused due to "user error" or because the person using the computer wasn't careful enough. That statement is only partly true. Even if you have all the latest Windows updates installed and are using the latest version of a secure browser, there are always some vulnerabilities can be used to attack your computer. Good anti-virus software stops you from downloading viruses or opening unsafe files. That's why it is essential to have anti-virus software installed and updated.

Many computer dealers will ask you to buy a licence for an anti-virus suite along with the PC, but free anti-virus software along with an anti-malware programme form a line of defence that's good enough for most people.


Panda Free Antivirus 2016

Like Avast, Panda scored top marks for virus protection in AV-Test's report. Its interface is pretty but not as user friendly as that of Avast. It also has a nice feature called USB Vaccine - this prevents virus attacks that occur when you plug in an infected USB drive.
http://download.cnet.com/Panda-Cloud-Antivirus-Free-Edition/3000-2239_4-10914099.html Download


Avast 2016 Free Antivirus

Avast is easy to understand, uses simple language to explain any problems, and has a great user interface that anyone can follow. It simplifies things like updating to the latest version and keeping the virus list up to date. Use silent mode to avoid the excessive announcements.
Download https://www.avast.com/en-in/download-thank-you.php


BitDefender Antivirus Free Edition

BitDefender's best feature is that it runs quietly in the background by default. It won't bother you until it spots an infection, unlike most other anti-virus software, which need a fair bit of tweaking to get them to stop popping up all the time.
Download http://www.bitdefender.com/solutions/free.html
If your PC is already infected
The software mentioned above are great if you install them before your PC is infected. Once there's a virus attack, it can get tricky to get install these programmes especially if system functions have been hijacked by the virus. Anti-virus software can still help, but malware removal tools are more effective in cleaning up your computer once the infection has set in


Comodo Cleaning Essentials 6
Malwarebytes was, in our experience, the best tool for malware removal, but it still requires you to install it on your infected PC. Installing software may not be possible in some heavily infected machines. In such cases, Comodo Cleaning Essentials 6 will be useful. You just need to unzip the file to use this set of virus cleanup tools. Comodo Cleaning Essentials 6 is portable software that runs without installation, making it useful in worst case scenarios.
Download https://www.comodo.com/business-security/network-protection/cleaning_essentials.php

Anti-virus software, along with a malware cleanup tool should be good enough for most users. You can pick any of the software listed above for protection against threats, and feel secure when using your computer, without having to pay a small fortune for the software.

Malwarebytes Anti-Malware

Malwarebytes Anti-Malware is a very effective tool for getting rid of a virus that's already made its way into your system. It's not useful for protecting your PC from virus attacks as it doesn't offer realtime threat protection, but is excellent at cleaning up the mess.
Download
http://www.malwarebytes.org/mwb-download/

Source: http://femdevcon..com/2015/02/if-you-have-windows-computer-you-need.html?m=1

Well all these are best free antivirus but kaspersky is also a better option in free antivirus.

femdevcon:
If you have a Windows computer, you need anti-virus software. There always will be those who will insist that every virus attack is caused due to "user error" or because the person using the computer wasn't careful enough. That statement is only partly true. Even if you have all the latest Windows updates installed and are using the latest version of a secure browser, there are always some vulnerabilities can be used to attack your computer. Good anti-virus software stops you from downloading viruses or opening unsafe files. That's why it is essential to have anti-virus software installed and updated.

Many computer dealers will ask you to buy a licence for an anti-virus suite along with the PC, but free anti-virus software along with an anti-malware programme form a line of defence that's good enough for most people.


Panda Free Antivirus 2016

Like Avast, Panda scored top marks for virus protection in AV-Test's report. Its interface is pretty but not as user friendly as that of Avast. It also has a nice feature called USB Vaccine - this prevents virus attacks that occur when you plug in an infected USB drive.
http://download.cnet.com/Panda-Cloud-Antivirus-Free-Edition/3000-2239_4-10914099.html Download


Avast 2016 Free Antivirus

Avast is easy to understand, uses simple language to explain any problems, and has a great user interface that anyone can follow. It simplifies things like updating to the latest version and keeping the virus list up to date. Use silent mode to avoid the excessive announcements.
Download https://www.avast.com/en-in/download-thank-you.php


BitDefender Antivirus Free Edition

BitDefender's best feature is that it runs quietly in the background by default. It won't bother you until it spots an infection, unlike most other anti-virus software, which need a fair bit of tweaking to get them to stop popping up all the time.
Download http://www.bitdefender.com/solutions/free.html
If your PC is already infected
The software mentioned above are great if you install them before your PC is infected. Once there's a virus attack, it can get tricky to get install these programmes especially if system functions have been hijacked by the virus. Anti-virus software can still help, but malware removal tools are more effective in cleaning up your computer once the infection has set in


Comodo Cleaning Essentials 6
Malwarebytes was, in our experience, the best tool for malware removal, but it still requires you to install it on your infected PC. Installing software may not be possible in some heavily infected machines. In such cases, Comodo Cleaning Essentials 6 will be useful. You just need to unzip the file to use this set of virus cleanup tools. Comodo Cleaning Essentials 6 is portable software that runs without installation, making it useful in worst case scenarios.
Download https://www.comodo.com/business-security/network-protection/cleaning_essentials.php

Anti-virus software, along with a malware cleanup tool should be good enough for most users. You can pick any of the software listed above for protection against threats, and feel secure when using your computer, without having to pay a small fortune for the software.

Malwarebytes Anti-Malware

Malwarebytes Anti-Malware is a very effective tool for getting rid of a virus that's already made its way into your system. It's not useful for protecting your PC from virus attacks as it doesn't offer realtime threat protection, but is excellent at cleaning up the mess.
Download
http://www.malwarebytes.org/mwb-download/

Source: http://femdevcon..com/2015/02/if-you-have-windows-computer-you-need.html?m=1

Kaspersky recently launched a free anti virus software - really good:
https://www.themaiguard.com/2017/07/kaspersky-now-offers-a-free-antivirus-software/