There are tons of free antivirus out there but a free software usually doesn't suffice. The stronger antiviruses usually demand annual payment from its users and gives only a 1 month free trial. When you try searching for the best antivirus for PCs, review pages would only be giving you a single brand, Bitdefender.
I found out that Bitdefender 2018 is actually giving a free 3 months trial. Whether you intend to buy the software and wanted to try the program first or you find a trial sufficient to clean your virus infested device, 3 months is more than enough to satisfy either needs. What’s more, a single account can install the program in 5 devices. The probably won’t last so you better grab the free trial as soon as possible.
Here's the link:
https://www.bitdefender.com/site/Facebook/redFreeDownload
For someone who can't afford to buy the full software, I've been using the free 3 months trial to clean my PC of viruses my previous antivirus failed to get rid of.
Installed it on July 22, 2017, that's why there are only 78 days left.