Here is how you get malware/viruses on your computer and have your passwords stolen(excerpt from malwarebytes.org):
Just For Men website serves malware
Posted September 20, 2016 by Jérôme Segura
“The website for Just For Men, a company that sells various products for men as its name implies, was serving malware to its visitors. Our automated systems detected the drive-by download attack pushing the RIG exploit kit, eventually distributing a password stealing Trojan.”
So which anti-virus should you use? Well, there is no such things as the perfect anti-virus but my favorite is Malwarebytes AntiMalware. You can get your copy here. This is part of what I use to clean up customers virus/trojan/malware infected computers.