Problem with google and advertisements

So there are a bunch of websites I always go to and I have noticed over the past 2 weeks that every once and a while I will open up safari and go to these websites and every advertisement is one of 4. They are all annoying... one flashes saying "congratulations you've won!". Another is a full fledged commercial that I can not turn off. At the same time, when I go to google and try to search for things, I click on a link and it opens a new window with some random site (not what I clicked). If I close that window and click on the link again, it directs me to the right page. I went to the apple store about this and they just told me thats normal annoying ad stuff. I realize ads are annoying but I use the internet a great deal and have never seen anything like this before. Any help would be greatly appreciated!