Messenger Live Hack Help

[SRRAE]

Hi,
It seems I keep getting messages from my Dad's messenger account which is obviously a bot which is sending replies trying to get me view a Yahoo account.
It starts by saying "Hello there " and no matter what you reply it will reply with something about dating sites etc.

Now these messages are appearing from him when I am logged on to a PC or on Xbox Live.

When my dad finally does log on to messenger live he can sign out of a computer called Home-PC which is not his computer.
Doing that stops the messages for a few mins before they sign on and start messaging again.

From from my wife's netbook, which my dad or I have never used, I did a password recovery for my dad's live account and changed the password to a random generated password.

5 mins later his account was logged on again and the messages started appearing again.
Since then I have changed the PW and username again on a different PC and 5 mins later he appears online on my account and about dating websites.

I have also changed my username and password on messenger, and still Im getting the messages.
I have reported it to MS but its still worring.
I dont think the account is hacked, but some how the account is being spoofed.
Any ideas what I can try next?

 

[hang-the-9]

Make sure you run virus checks on all of your computers. MS support will need to check why his email is sending stuff out even when he password is changed.

 

[SRRAE]

I am now not dismissing they are not in fact logged on as my dad, but a computer has a virus which is spoofing the conversation.
It seems the conversations only happen when one computer is turned on. When this computer is turned off it doesn't seem to happen. Turn this computer back on and the conversations seem to start up again.

I have done a full sweep of the computer using Microsoft Security which found nothing. I am currently using the one supplied by my ISP which is a Trend Micro.
Which other anti virus can people suggest which may give the best results?

 

[hang-the-9]

Run Malwarebytes also.