Every website has a metatag attached to it.
A sex site will have metatags such as sex, nudity, it's a way of identifying what that website is.
If you went to google and typed in words, google checks for metatags first, then content.
Your company probably has a blocking tool, called websense. It blocks certain types of websites, ie. gambling, nudey etc.
You can also use a private browser like Tor Browser.
There is no way to get round this These types of sites are usually blocked from network administrators, because i am also a network administrator i know how to see these sites.
You can also see how to assign an Ip address in Windows 7
Just open any search engine like Yahoo or Google and in search field write your site address and click search in results you can see the your site name listing just click on your desired site and enjoy surfing. this happen because your network admin cannot watch your surfing activities because these sites are not opened directly you can try megaproxy.com its a nice side but from all this side if u are browsing anyother side and in tat side if you are giving any username and password kind of thing then it'll not work becouse for that u have to pay some money to this side then only they will give you 100% access free of cost u can open the side but can't check u'r mails or personal things.The website u r talking about might be very wornderful n it might ask u to give the credit card number. If u really wish to see the website like this u better send them the cash not the cheque or card number, Otherwise they'll cheat u.