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Welcome to the forums, avnguyen.
First, there is very little information to go on ... what program/file/warnings/etc ... nor what OS your computer has. But, I am guessing you have some type of trojan that is sending out email.
For W2000 & XP, try using Ewido as it is very good with trojans.
For W95, 98, ME try using a-squared.
If this is not the problem, please post more information.
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