Computer viruses primarily come from one main source, websites. Sometimes, you’ll get a virus upon launching a website while other times the virus will appear after opening a link from a site. More chances than not, if you have a virus, it’s from going to a website that already has a computer infection.
So, if you are the type to perform proactive computer maintenance, or more notably, pre-emptive virus attack missions, you should install WOT, or Web of Trust. It is compatible with Firefox and Internet Explorer, not with Chrome and Safari. After you install it, all future sites will be measured for any maliciousness. In turn, you’ll see a green circle that rates it as safe, red means stay away, and yellow is use at your own risk. It’s like the level of alert system in NYC, but applied to online threats and risks.
If you’re the type who is susceptible to getting computer viruses, or just want to protect your computer, using WOT along with a solid antivirus software is a great security measure. Google will sometimes show if a site is safe or not, but not all the time. WOT give you around-the-clock warning of any bad sites. Keep in mind though that it is up to you to not launch these bad sites. WOT can only lead the horse to the water, but it is up to you if you want to drink it or not!