I am understand that there many free antivirus softwares available online. I am bit confused with which one to go. While I downloaded Avast and installed, it really took much of my bandwidth. I tried closing all auto updates and even after that, when I connect to net, it automatically starts eating up my bandwidth, which I don't like and want to avoid. So, I uninstalled the Avast. I want expert advice at free of cost. thank you in advance.

Please take a look at http://forums.dlsoftware.net/spyware-anti-virus-tools-f40.html there may be something there for you