Has my Hotmail account been infiltrated?

Hi I have a serious problem that I believe may be some form of identity
theft and breach of security.

I have been informed by a few people that I know that they have
received emails, allegedly from me, which usually have the following
traits:

1. they are from my Hotmail account and name, although the name on
these emails has only my first initial instead of my full name that all
my email accounts and client are set to

2. they are usually blank, but one or two reports that they had
attachments

3. the subject line includes the phrase "Not read:" and is often
followed by subject line text that had been in previous emails between
myself and them.

I am using a Mac with Microsoft Entourage as my primary email client. I
have run both Norton Antivirus and MacScan and have found NO viruses,
spyware or keyloggers. I have turned on OS X's firewall and I
frequently clear all my browser caches and cookies. I have changed my
Hotmail/MSN password. So far, this did not solve the problem.

I do not use forwards nor multiple-address emails, and my contacts have
zero connection to each other except through me. They do not receive
emails from each other nor have each other as contacts. The only
connection is through me. Does someone have access to my address and
contacts somehow? This is very worrisome, your help is greatly
appreciated... I have not received any response from Microsoft Security
and this is very frustrating... I am worried someone can do some real
damage.

.

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