I have reason to believe that someone has stolen my cookies and now i have some questions.

Is it possible that someone could place a cookie grabber on say the main menu of a forum and then get all my cookies?

Could those cookies then be used to show that person what web sites i visit, and be used to track my activity online?

Could the person who stole cookies then gain access using my username and password and cookies to other web sites?

If they can get access is deleting cookies and changing my password enough to stop them from accessing it again or will the old cookie still work?

Is there some other way they could access anothe rsite i use and get information about who is there and ip addresses?

Some web sites won't work if cookies are not allowed. How to i protect myself from cookie grabbers when cookies are essential and convenient?

I use adaware, anti virus software and a firewall, is there anything else i should be using to prevent security breaches?