Hi abbie, moved topic to Off-topic Lounge since it's unrelated to GES.
As for Anti Virus, you should read some of the IT magazines tests and decide which one is the most suitable for you.
Most of them are doing a good job in recognition rate, some have a bigger impact on system performance then others and since they're free you have to get used to some advertising once in a while.
Depending on the AV and sensitivity you choose, there might also be some false positives sometimes.
Some of them even could be called scareware, since they alert stuff that isn't a virus but software that some companies don't like to see used.
e.g. i had false alerts on some emulator software with Avira.
However the best protection beside FW and AV still is your brain.
Use webmail services rather then MS Office or other mail apps that download mail content directly to your computer even before viewing it.
Stay away from illegal stuff and also pay attention if you use free services or free software/shareware, most of them try to gift you a few additional but in most cases useless programs.
I once had to clean up the PC of my step grandpa, which had a serious amount of toolbars and other stuff that was slowing down the machine a lot.
