I checked your site http://sitecheck.sucuri.net/results/...teverfree.com/
and it looks clean.
If you're using Firefox, I have the same problem with it randomly opening new tabs to spammy websites. It doesn't matter which website I'm on at the time.
I know my sites are clean and I've done various virus and spyware scans which all came up clean. I suspect it's Firefox as it stopped happening when I switched to Chrome.
Maybe you have a different problem, but it sounds the same as mine.