Do I need to buy an anti-virus program?
No, you do not need to buy or renew an anti-virus program. However, keep reading. You do need an anti-virus program on your various computer devices, including PCs, tablets, and phones.
You will see notices appearing to renew your McAfee antivirus and other products. I use them as an example as it seems to pop up several times a day on my computer and I have never used their product for my personal devices (one college I worked at used their product and had it on my office computer).
You can use various free anti-virus programs and they perform as well as paid products in most cases. Most of them will also sell you an anti-virus program that comes with bells and whistles that may interest you, but you can get good basic protection for free.
The two ant-virus programs I currently personally use are Avast and Immunet. Both are good products and I see them catch things and remove or quarantine from my systems. I use Avast on both my phone and PC. AVG, Kaspersky, TrendMicro and others are available and have good reputations. Microsoft includes Defender for free with Windows and it is running on my PC, but I have never seen it catch anything, which raises doubts in my mind. Malwarebytes has a free version but requires you to do manual scans. McAfee gives a free short trial then charges. Norton charges from the start. Back when there were no free anti-virus programs, I loved Norton (although it had a few bad releases). I am not a supporter of McAfee, as I have seen it let things by too many times and it is only available for a fee. Immunet uses an antivirus engine by Cisco, and I have recently started playing with it and I have seen it catch items.
There are lots of free choices with anti-virus programs, so it is what you prefer. Everyone has opinions on the best and now you know mine. The important thing is that you have a current antivirus program on your computer, and it be kept up to date with the latest definitions/ signatures and monitors all the time.