Sites blocked???

No, someone would have had to open your Network preference panel and changed the DNS settings. Open your Network preference panel, click on your active connection (usually Built-in-Ethernet), click on Advanced, click on DNS, and tell us what you find there.

Since you mentioned "adult" sites it is also possible you picked up a known trojan horse that alters your DNS entries. But instead of blocking your access to adult sites it's function is usually to force you to them. This trojan horse would have been disguised as a video player or codec. You would have downloaded it and installed it thinking it was needed to view a video. See this article from MacWorld...

http://www.macworld.com/article/60823/2007/10/trojanhorse.html

Message was edited by: lkrupp

From the url you posted it appears you are using OpenDNS as your DNS server. There are a number of posters on these forums who are always recommending people change their DNS servers. Did you or someone else with administrator privileges change the settings? Open DNS (this is not software on your system. It is a company that provides DNS services) also allows filtering or blocking. Do you control your network or does someone else?