Over the years I have used many different antivirus programs. I feel this has given me the education, experience and authority to recommend the following programs. Many of the programs below also have paid versions but I have found that there is no need to purchase them as the added extras are often not needed.
AVG is a fantastic little piece of software totally free of charge. The current version AVG Anti-Virus Free 2012 is probably the best version to date. It provides full protection against viruses and spyware and also boasts free 24/7 support. It is thought that over 100 million people use AVG at the moment and it is probably the most popular of all free antivirus programs.
Avast free anti virus is similar to AVG. The free version comes with an engine that blocks viruses and spyware and also offers remote connections so that you can get help from a friend or techie if needs be. Avast claims that they have over 150 million active users which cement its popularity throughout the world.
Adaware made by the software company lavasoft primarily started off as an anti spyware program but has now also branched into anti virus. Amongst others it features a download protection that identifies malicious files that are being downloaded onto your computer. It also features a sandboxing feature that allows you to run malicious files in a virtual environment. It is one of the most powerful free antivirus programs about. To date there has been about 400 million downloads of their free software.
Malwarebytes is probably my favorite all time anti spyware program. Over the years it has built up an excellent track record removing spyware for me and it has built up a fantastic following amongst techies. It proves to be extremely efficient removing Trojans and root kits. It uses a sophisticated method of removing malware not seen in other free programs. To date there has been about 100 million downloads and it has successfully removed over 5 billion pieces of malware.
Spybot Search and destroy
Spybot search and destroy free edition is an extremely efficient and effective piece of software. It was developed by a world wide team of software specialists with a strong background and education in malware and spyware technologies. It is 100% free for private use. It can also clean usage tracks which is useful if you share your computer with other people.