Another problem is that people can also use software and proxy servers to mask their true IP address.
"You can use a proxy machine, meaning instead of connecting directly from my computer, I connect to another computer and from there I make those posts," says Christin, who notes that it's "relatively easy to anonymize" your traffic on the internet.
People could also use something like the Tor network, free online software that Christin says is fairly easy to download and is "essentially a peer-to-peer network that is not used for file sharing. It's a peer-to-peer network that is used to anonymize data over the internet."
Say someone used Tor to go to the CBC.ca website and post a comment the CBC.ca website, instead of seeing the IP address of the actual machine from which the visit is coming would see the IP address of one of the machines that participates in the Tor network
Finding the true IP address in that instance "is going to be essentially impossible," says Christin.
http://www.cbc.ca/news/canada/story/2012/10/16/f-tracking-online-identity.html