Why I have an unknown user accout automatically?

From: Edward (whq@hotmail.com)
Date: 09/30/02 

From: "Edward" <whq@hotmail.com>
Date: Mon, 30 Sep 2002 10:49:46 -0700

Today I found an unknown user account in Control Panel ->User Accounts. This
is my second time for discovering an unknown user account. The first time I
deleted the account.

Is somebody hacking my computer? How can I prevent it from happening again?

Thanks

Edward