This is a list of free antivirus solutions. Each one has their strengths and weaknesses and you will have to do a little research to know what is best for you. Personally I use Microsoft’s Security Essentials because it works well for me, however I am not recommending it as there are a number of options some of which might be better given your needs. The three below I have used and had reasonably good experiences are Avast, AVG and Microsoft Security Essentials. While I have not used Bitdefender for Windows (it does have generally good reviews and my experience with using their Linux Freeware version is good.
- Avast Free Antivirus
- AVG Free Antivirus
- Avira Free Antivirus 2013
- Bitdefender Antivirus Free Edition
- Malwarebytes Anti-Malware Free
- Microsoft Security Essentials
- Panda Cloud Antivirus Free
One note of caution. Read the licensing agreement. Most are free for personal use (home), only some are free for business or corporate use. It is highly recommended to choose an antivirus solution that provides real time protection.