You may have been hijacked by a dialer. If you have a dialup modem I would call AT&T and see what they had to say. Also you can check this site out to see what else to do.
http://clarkhoward.com/topics/porn_charges.htmlHere's how it works...
1) The consumer - usually a teenager - logs on to a computer and accesses a pornography site through his or her Internet Service Provider (ISP).
2) A teaser Web site then downloads "dialer" software onto the consumer's computer.
3) After "dialer" software is activated, the consumer's computer modem disconnects from the ISP and dials an international telephone number assigned to Madagascar, Vanatu or another distant foreign country.
4) The consumer then returns to the Internet through an ISP purportedly located in Madagascar or the foreign country initially called.
5) The consumer's Web site is directed to an adult-content Web site hosted on a computer in the United States.
6) You are billed at up to $7 to $8 dollars a minute and the charges appear on your AT&T bill. Keep in mind that you don't have to be an AT&T customer to be a victim.
Here are two programs that will help you ..
Ad-Aware
http://majorgeeks.com/download.php?det=506Spybot S&D
http://www.safer-networking.org/en/download/index.html