When I surf on net, suddenly open unwanted site. Is it virus? How can I remove it
Install Spybot Search&Destroy and run a scan once
It a Spam go and install any AntiSpam software and run full scan once.
you are infected by some adwares.Do full system scan with one good antivirus+2 good antispywares.
Remember to turf off system restore brfore you do scan.Also prefer to do scaning in safe mode..and if possible do a full online system scan.