Deswal ji
I used 3-4 anti virus(with license version)
1- Nortan Anti Virus - performance good ,speed slow
2- Symantec - Performance Good,speed better compare nortan
3- Quick Heal - Performance Good,speed Good, on site support
4- Avg Antivirus - Performance Good,speed good
TODAY i think best Quick heal.......
Frist start combofix downlaod this link http://www.combofixdownload.com/
and than scan ur pc any antivirus.....speed increase