How to remove muti.dll threat frm my sytem, i already had antivirus software(updated)?

I am not fmailiar with this singular dll

However, I would have to question what antivirus you are using AND since a lot of browser objects which can turn out to be spyware or adware come in dll's I would question whether or not you have used the proper tool.

I would suggest you purchase a security suite (a/v, firewall, antispyware) from a reliable vendor (like mcafee) and properly configured it and automatically updating... then perform a complete scan.

If you already use a reliable vendors product make sure it contains an antispyware antiadware feature or upgrade to it.

You can also try Spybot S%26D from http://www.safer-networking.org which will remove spyware/adware and protect against it.

Good Luck