My laptop is being bombarded by Norton Internet Security risk / anti-virus alerts. How do I get rid of these ?

Please help. My laptop is being constantly bombarded with messages saying " Insecure Internet Activity, Threat of Virus Attack " and " System Infected - Trojans, Worms, Spyware " etc. Every time I wish to visit a website my screen is filled with these messages, Im given the option to " Click here to get full-time advanced real time protection and continue browsing " ( Im then taken to a credit card / purchasing screen ) or to " Continue to this website unprotected ( not recommended ). I have removed the Norton Internet program yet they are still bombarding me with these screens / messages. Any advice is much appreciated.