Note that many websites have their own advertising, unrelated to adware.
From http://www.symantec.com/security_response/writeup.jsp?docid=2004-112213-4204-99 :
"The Netster Smart Browse toolbar:
* Is an Internet Explorer toolbar with spyware-related functions.
* Has replaced the Internet Explorer search destination to netster.com.
* Tracks usage of search queries, clicked links on the toolbar, as well as search terms and other information in the netster.com server logs, which netster.com uses to better tailor future advertising content.
* The user names and email addresses can be taken from several opt-in parts of the toolbar and given to third parties for advertising purposes."