It is very important to hide your IP, when you are surfing. Your IP will be logged from the most servers and this log files can be checked by the FBI. So they can find out, which user made which posts.
You can see your IP here: http://whatismyipaddress.com
A very good secure and free proxy is the TOR Network. The easiest way for beginners to use TOR is the Linux distribution TAILS. Download it and burn a CD. Boot from this CD and you have an easy way to surf anonymously in the web.