The are many good free antivirus protection programs available. Some are Open Source and others are freely available for personal use. I used F-Prot for many years back in the DOS days when I was running a BBS. F-Prot was fast and easy to use and you could automate it with DOS to do regular scans of incoming files. Clamware is an Open Source Linux product that is widely used but lacks some of the features of newer commercial products. Avast and Avira are also highly rated along with Panda, AVK, and BitDefender, but AVG basic free is still my choice. I have been running it for years now with never a concern. I have had some nasty viruses in my labs over the years but AVG has kept them all at bay. Before using AVG we had a boot sector virus that got onto all the student disks and flash drives. We had the hardest time trying to get rid of it until we began imaging our computers. Using images, you can quickly restore back to a know good configuration. I been in other labs where the teachers have given up trying to rid the computers of viruses. It really isn’t that hard to keep your computers running at their optimum and free of viruses. Using some good freely available tools you can manage hundreds or even thousands of computers quite easily. I have successfully managed over one thousand computers at seven different sites using just imaging tools. I took me over a month to get around to each computer and I would do regular restores that would rid the computers of 99% of the reported problems. This kept my trouble shooting times down to just a few minutes each day for replacing power supplies, hard drives, and CDROM drives. Over 90 percent of all the computer problems you will see are related to software. Windows will continue to be the operating system of choice and they keep me busy making a good living. Mastering the beast is the key and there are some good tools available like free antivirus protection software.
The Best Free Antivirus Software website has some additional information you might find useful.