As today we can see lots of viruses in the internet world; malware, viruses, adware, spyware and much more when they capture our computer we feel like hell.......many peoples get technical advise on that time which is good if you don't know about it. What you do???
If they've captured it, I'd rush to the store to buy strong stuff to destroy them. Anyway, this situation never comes up with people who don't surf vulnerable websites and/or have some sort of protection.
A free antivirus is generally sufficient to keep you safe, they still update with the same database the paid one has, it's not like they restrict what you are protected from just because you went for a free option, unless it's a dodgy company. You probably also want some form of firewall, the built in Windows one can often be good enough to give you decent protection for day to day use.
It all comes down to your browsing habits and what you do on your computer, to stay protected, you also need to teach yourself to look out for links to not click and attachments to not download. Most of the time when people get infected, its not because of a lack of antivirus or security, it's simple user error.
