Thanx Bob,Tech,Charley0,DavidR,Alanrf for all your guidance.My system is clean now & i've installed latest version of avast antivirus.Everything is back to normal.Thanks to you guys,i came to know about so many new softwares & other similar stuff.Anytime in future also if i or any of my friend encounters such a situation,the guidelines given by you all will prove so very useful.I would like to once again thank you all for your co-operation without which i wouldn't have been able to put all the things in place.