While we are talking about Virus and Virus scanner in this Topic, I want to kind of hijack and use this to advise everyone to have a decent Antivirus and Firewall running on their PCs.
Not having any protection here is highly careless. A lot of sites have trojans, viruses or even just malicious cookies that install themselves on your PC without you ever noticing it. This is especially true for sites offering porn! It may not only lead to you having to reinstall your Operating System, it can go as far as getting confidential Data from your PC, get access to your webcam (with videos being posted around the web, it became quite the sick "sport" in the past couple of years) without your noticing, getting password to your favourite Online Game or Site or theft of Credit Card information.
AVG is a decent free solution as is Avast! in addition to Microsoft Security Essentials. This is the bare minimum of protection you should have. If you want a better solution I'd advise Bitdefender Total Security, which not only has extensive options if you're a pro, it also has very good standard configurations, guides you through everything and identifies security risks in your windows settings, is very low on ressource, has a mode called gaming mode (which pauses the virus scanner whenever you tab into a game and enables it back when you are out of it) and a lot of 1 click solutions if something goes wrong (including a one click reinstall if the virus damages the scanner). The latest Kaspersky also seems to be quite good, although Bitdefender has been winning most awards 3 years in a row now.
Both have 30 day trial versions available on their manufacturers webpage.
In addition you should always have some kind of Malware Scanner, like Malwarebytes Anti-Malware or Ad-Aware and Anti-Rootkit like Avast!.
Even though these programs offer a decent amount of protection, you are never 100% secure. But if someone wants to steal from you, you can either have a thin wooden door with the key left in it or have a steel door locked with multiple high security locks. Guess what is harder to open ...