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.