2. Use the following scanners to find and remove the website.
SpyBot S&D searches your harddisk for so-called spy- or adbots;
http://security.kolla.de/
or
Adaware
http://www.lavasoftusa.com/software/adaware/
or
CWShredder
http://www.spychecker.com/program/cwshredder.html
3. Some porn websites redirects links to their websites using your HOSTS
file. Do a search for the HOSTS (without extension) file and remove the
entry.
4. If still no joy, download HijackThis from Spywareinfo download page
http://www.spywareinfo.com/downloads.php
Run the program and you will find many entries. Most are OK. Post the log. I
will find the problem for you.
5. For future preventive maintenance, make sure programs cannot just
download on your computer without your permission. From the Internet
Toolbar, go to Tools > Internet Options > Advanced. Make sure "Enable
Install On Demand (Internet Explorer)" and "Enable Install On Demand
(Other)" are unchecked.