We tried the AVG free... and while it seemed to work, I think there might have been some minor glitches with our old Windows XP. And, the free version is limited... You will not actually see it, but there could be a lot of other invasions, spyware, etc.. on your computer.
We had tried BitDefender... Glitches with it with our Windows XP.
Then, downloaded the free trial of CyberDefender to try it. Again, it seemed to work, but the free version is limited.
We now realize that for full protection, one must pay for a full package.
In almost every single case, the 'free' version is just a limited teaser, and you will be heavily encouraged to purchase the better package.
We now have Eset... We haven't had it for long, (bought it off
Amazon a few weeks ago) but it is virtually invisible, and doesn't seem to be a huge drain on our poor old outdated system. When we installed it and ran the full scan for the first time, it flushed DOZENS of hidden viruses and spyware etc. from our system that one can only imagine the prior programs had missed!!!!