It sounds like your browser is susceptible to nasty stuff getting in there, are you using Internet Explorer? You may want to switch to another browser, like Firefox
http://www.getfirefox.net/I use Opera and it is even faster than Firefox but is not quite so well-known
http://www.opera.com/browser/download/And others use Chrome but I hate it as it is far too minimalistic, I like lots of buttons and things to click on (that's why I like Opera)
www.google.com/chromeBut there is something that's gotten into your pc in the first place, probably via Internet Explorer, because spyware, malware and trojans / ad-popups etc all use exploits within the 'Active X' coding within IE which other browsers don't have. So you will probably need some antispyware programs to clean out your pc. First, do a virus scan with your antivirus program (if you don't have one, you can downloiad Microsoft Security Essentials for free -
www.microsoft.com/security_essentials/ - I use Avira Antivir -
http://www.free-av.com/ ). Then do a cleanout with an antispyware program like Malwarebytes
http://www.malwarebytes.org/ and then use the C Cleaner
http://www.piriform.com/ccleaner/downloadNow if you do all of that and start using a new browser, then you should be fine. Failing that, ditch Windows altogether and download the latest Linux Mint 10
http://www.linuxmint.com/download.php and never ever have to worry about getting a virus or trojan ever again! The latest Linux operating systems are now equally as good as Windows, easy to set up, and completely free! I recently did this for some friends who got attacked with a severe virus and they are very happy with Linux.
Regarding porn itself, I recently watched a 3 hour documentary 'The Kinsey Syndrome' and it was the saddest and most sickening thing I've ever watched. You can watch it here on YouTube
http://www.youtube.com/watch?v=rAvF23WvoUc - it's about the famed 'scientist' Dr Alfred Kinsey, whose work laid the basis for the sexual revolution in America and the basis for sex education in America, and in partnership with Hugh Hefner, was responsible for the proliferation and making pornography 'normal' in America and around the world - to what we see on the internet today. Now, what people don't know, was that thousands of children (funded by the Rockefellers, the US govt and Indiana University) as young as 5 months of age, were raped and abused by pedophiles with stopwatches, with their parents in total support of the whole sordid thing. Truly the saddest thing I have ever seen.. they even interview children (now in their seventies) who were involved with it. It's totally changed my perspective on pornography and the evil agenda behind it. They talk about Aleister Crowley and Kenneth Anger being close-knit with Kinsey, as well as a high-ranking ex-Nazi general who was raping/molesting/killing young children in the concentration camps in WW2 and somehow made his way over to America and became part of Kinsey's program. Incredibly detailed and well-researched documentary, a terrible truth to swallow.
I see these porn popups as a symptom of Kinsey's evilness - that it has proliferated to such a point where it can innocently turn up on someone's computer where it is unwanted.
Anyway, good luck with your pc, best of luck to you!