You get CL for free because of supporting vendors and advertisers
1) If any of the ads bother you, I'd suggest you install and use an adblocker plug in. Several threads here discussing some good ones; I use AdBlock
2) Many of the advertisements on the forum don't show up when you are logged in, suggest making sure you are browsing that way.
3) Some ads as you describe it above may be coming from adware installed on your PC and not from CL. Run an adware/spyware scanner.