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.
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.
There are plenty of sites out there to provide you details of WHY Malware is such a concern today so I am not going to repeat the message here. I am assuming you already know what Malware is and are looking for a simple list of things you should do to protect yourself. If I am assuming correctly then I expect you will like this list.
How to Protect Yourself from Malware
Keep your system up to date. Apply related security patches as soon as they are available. This is for both your Operating System (including things like Linux, Windows, iPhone, iPad, Surface, Android, etc) and the applications that are on the system.
Install a strong antivirus software solution and most importantly, KEEP IT UP TO DATE. It is good to periodically run a full system scan.
Remove applications you are no longer using and will not be using.
Do not install applications from locations you do not trust. This includes locations such as peer to peer sharing, pirated software, FREE songs that should not be free, companies you do not know or trust, emails from unknown senders, unexpected emails from senders with suspicious content, etc.
Do not use USB or USB type devices from untrusted/unknown sources.
Do not open files sent through Instant Messengers from untrusted/unknown sources.
Use a proxy with Malware protection. Ensure it is regularly updated and includes the ability to examine all content (including SSL traffic) and provides regular block list updates for known “bad” sites.
Use additional browser plugins such as WOT (Web of Trust) or Bit Defender as a way to know site ratings from web searches prior to clicking links. WOT is a great source for user feedback, you can even provide your own feedback for any site!
Use your browsers built in phishing and Malware protection services. If your browser does not offer this I suggest using a different browser.
Do not run your browser as an “Administrator” or using elevated credentials.
Do not use SSL (HTTPS) sites with untrusted certificates.