I keep getting these alerts from messenger

From: Aman (sweety_rishi@hotmail.com)
Date: 12/09/02 

From: "Aman" <sweety_rishi@hotmail.com>
Date: Mon, 9 Dec 2002 11:33:17 -0800

Hi All,

I installed Window 2000 (upgraded from Win Me) and since
then I keep getting these annoying alerts/messeges "buy
this/that or visit this site"

How can I stop this nuisance ?
Is this a security flaw in Win 2000 (since I never had
such problem with Win Me)

Please advise.
Thanks you all so much !
Aman