Antivirus software is only as good as the last person that touched it. I made a very good living mostly patching and repairing software for over 28 yrs fixing other programmer's mistakes. With the exploits today, there is no guarantee. Simply not running an account that lacks "admin rights" is no guarantee. Google it up for yourself.
At any one time, any of the AV programs will let something through or kill your machine itself based on a faulty update. Norton has done it, etc.
I run MacAfee as Time Warner provides it free (this years contract), prior to this it was something else. I run redundant machines with my data backed up across my network, so it doesn't hurt me if I lose one machine but it is an awful aggravation.
I have a hardware firewall running, Windows firewall running, real time scanning, as much as possible, but as long as sites are using ads to bolster their bottom line, and not being careful as to who they allow in, once they are in and running, if the hack is good enough, they got your machine.
A good anti-virus (Google up reviews and read them) along with a good pop up ad blocker/killer will go a long way.
Use this as a Google (or whatever search engine you use) and do some reading "best popup ad blocker". (without the quotes).
I suggested using the Trend Housecall as a double check. It is not a primary antivirus product. It is a one time run to scan your machine as sometimes a good hack can get target your primary AV product.
I have AdBlock Plus installed now as I had gotten out of date since I don't work in the industry anymore. One of the folks on this (or one of the other sites) posted that up. It is working OK so far.